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Review Questions

Chapter 1_________________________________

<=
/o:p>

Review Questions

<=
/o:p>

1.Wh=
at is
the difference between a hypothesis and a theory?

2.Wh=
at is the
difference between a theory and a law of physics?

3.Ho=
w are
scientific theories tested?

4.De=
scribe
the role that skepticism play sin science.

5.De=
scribe
one reason why it is useful to have telescopes in space.

6.Wh=
at
caused the craters on the Moon?

7.Wh=
at are
meteorites? Why are they important for understanding the history of the sol=
ar
system?

8.Wh=
at makes
the Sun and stars shine?

9.Wh=
at role
do nebulae like the Orion Nebula play in the life stories of stars?

10.W=
hat is
the difference between a solar system and a galaxy?

11.W=
hat are
degrees, arcminutes, and arcseconds used for?What are the relationships among t=
hese
units of measure?

12.H=
ow many
arcseconds equal 1°?

13.W=
ith the
aid of a diagram, explain what it means to say that the Moon subtends an an=
gle
of ½=
°.

14.W=
hat is
an exponent?How are exponent=
s used
in powers-of-ten notation?

15.W=
hat are
the advantages of using powers-of-ten notation?

16.W=
rite the
following numbers using powers-of-ten notation:

&nbs=
p; &=
nbsp; (a)
Ten million

&nbs=
p; &=
nbsp; (b)
Sixty thousand

&nbs=
p; &=
nbsp; (c)
Four one-thousandths

&nbs=
p; &=
nbsp; (d)
Thirty-eight billion

&nbs=
p; &=
nbsp; (e)
Your age in months

17.H=
ow is an
astronomical unit (AU) defined?Give an example of the situation in which this unit of measure would=
be
convenient to use.

18.W=
hat is
the advantage to the astronomer of using the light year as a unit of distan=
ce?

19.W=
hat is a
parsec?How is it related to =
the
kiloparsec and to a megaparsec?

20.G=
ive the
word or phrase that corresponds to the following standard abbreviations:

&nbs=
p; &=
nbsp; (a)
km

&nbs=
p; &=
nbsp; (b)
cm

&nbs=
p; &=
nbsp; (c)
s

&nbs=
p; &=
nbsp; (d)
km/s

&nbs=
p; &=
nbsp; (e)
mi/h

&nbs=
p; &=
nbsp; (f)
m

&nbs=
p; &=
nbsp; (g)
m/s

&nbs=
p; &=
nbsp; (h)
h

&nbs=
p; &=
nbsp; (i)
y

&nbs=
p; &=
nbsp; (j)
g

&nbs=
p; &=
nbsp; (k)
kg

21.I=
n the
original (1977) Star Wars movie=
, Han
Solo praises the speed of his spaceship by saying, “It’s the sh=
ip
that made the Kessel run in less than 12 parsecs!”Explain why this statement is obvi=
ous
misinformation.

22.A
reporter once described a light-year as “the time it takes light to r=
each
us traveling at the speed of light.”=
How would you correct this statement?

Advanced Questions

Questions prec=
eded by
an asterisk (*) involve topics discussed in the Boxes.

Problem-s=
olving
tips and tools

The small-angle formula, given in Box 1-1, relates the size of an
astronomical object to the angel it subtends.Box 1-3 illustrates how to conv=
ert
from one unit of measure to another.&n=
bsp;
An object traveling at speed v
for a time t covers a dista=
nce d given by d=3Dvt; for example, a car traveling at 90 km/h (v) for 3 hours (t) covers a distance d =3D
(90 km/h)

(3 h) =3D 270 km.=
Similarly, this time t=
i>
required to cover a given distance d
at speed

23.W=
hat is
the meaning of the letters R I V U X G that appear under some of the
figures in this chapter?Why =
in each
case is one of the letters highlighted?&nb=
sp;
(Hint:See the Preface that precedes Chap=
ter
1.)

24.T=
he
diameter of the Sun is 1.4 X 1011 cm, and the distance to the
nearest star, Proxima Centauri, is 4.2 ly.=
Suppose you wanted to build an exact scale model of the Sun and Prox=
ima
Centauri, and you are using a ball 30cm in diameter to represent the Sun. In your scale model, how far away =
would
Proxima Centauri be from the Sun?Give your answer in kilometers, using powers-of-ten notation.

=
o:p>

25.H=
ow many
Suns would it take, laid side by side, to reach the nearest star?Use powers-of-ten notation.(Hint:See the preceding question.)

<=
/o:p>

26.A
hydrogen atom has a radius of about 5 X 10-9 cm.The radius of the observable unive=
rse is
about 14 billion light-years.How
many times larger than a hydrogen atom is the observable universe?Use powers-of-ten notation.

=
o:p>

27.T=
he
Sun’s mass is 1.99 X 1030 kg. ¾ of which is
hydrogen.The mass of a hydro=
gen
atom is 1.67 X 10-27 kg.How many atoms of hydrogen does the Sun contain?Use powers-of-ten notation.

=
o:p>

28.T=
he
average distance from the Earth to the Sun is 1.496 X 108 km. Express this in distance (a) in li=
ght
years and (b) in parsecs.Use
powers-of-ten notation.(c) A=
re
light-years or parsecs useful units for describing distances of this size?<=
span
style=3D'mso-spacerun:yes'> Explain.

29.T=
he speed
of light is 3.00 X 108 m/s.&nbs=
p;
How long does it take light to travel from the Sun to Earth?Give your answer in seconds, using
powers-of-ten notation.(Hint:See the preceding question.)

<=
/o:p>

30.W=
hen the Voyager 2 spacecraft sent back pic=
tures
of Neptune during its flyby of that planet in 1989, the spacecraft’s
radio signals traveled for 4 hours at the speed of light to reach Earth. How far away was the spacecraft? Give your answer in kilometers, us=
ing
powers-of-ten notation.(Hint:See the preceding question.)

<=
/o:p>

31.T=
he star
Altair is 5.15 pc from Earth.(a)
What is the distance to Altair in kilometers?Use powers-of-ten notation.(b) How long does it take for light
emanating from Altair to reach Earth?Give your answer in years. =
span>(Hint:You do not need to know the value =
of the
speed of light.)

32.T=
he age
of the universe is about 13.7 billion years.What is this age in seconds?Use powers-of-ten notation.

=
o:p>

*33.=
Explain
where the number 206,265 in the small-angle formula comes from.

<=
/u>

*34.=
At what
distance would a person have to hold a European 2-euro coin (which has a
diameter of about 2.6 cm) in order for the coin to subtend an angle of (a)
1º?

(b) 1 arcmin?(c) 1 arcsec?Give your
answers in meters.

*35.=
A person
with good vision can see details that subtend an angle of as small as 1
arminute.If two dark lines o=
n an
eye chart are 2 millimeters apart, how far can such a person be from the ch=
art
and still be able to tell that there are two distinct lines?Give your answers in meters.

<=
/o:p>

*36.=
The
average distance to the Moon is 384,000 km., and the Moon subtends an angle=
of
½º.Use this
information to calculate the diameter of the Moon in kilometers.

=

*37.=
Suppose
your telescope can give you a clear view of objects and features that subte=
nd
angles of at least 2 arcsec.=
What
is the diameter in kilometers of the smallest crater you can see on the
Moon?(Hint:See the pre=
ceding
question.)

*38.=
On April
18, 2006, the planet Venus was a distance of 0.869 AU from Earth.The diameter of Venus is 12,104 km=
.What was the angular size of Venus=
as
seen from Earth on April 18, 2006?Give your answer in arcminutes.

*39.=
(a) Use
the information given in the caption to Figure 1-7 to determine the angular
size of the Orion Nebula.Giv=
e your
answer in degrees.(b) How do=
es the
angular diameter of the Orion Nebula compare to the angular diameter of the
Moon?

Chapter 2____________________________________

Review Questions

<=
/o:p>

1.Descr=
ibe
three structures or carvings made by past civilizations that show an
understanding of astronomy.

2.How a=
re
constellations useful to astronomers?How many stars are not parts of any constellation?

3.A fel=
low
student tells you that only those stars in Figure 2-2b that are connected by blue liners are part of the constellati=
on
Orion.How would you respond?=

4.Why a=
re
different stars overhead at 10:00 P.M. on a given night than two hours late=
r at
midnight?Why are different s=
tars
overhead at midnight on June 1 than at midnight on December1?

5.What =
is the
celestial sphere?Why is this
ancient concept sill useful today?

6.Imagi=
ne that
someone suggests sending a spacecraft to land on the surface of the celesti=
al
sphere.How would you respond=
to
such a suggestion?

7.What =
is the
celestial equator?How is it
related to the Earth’s equator?How are the north and south celestial poles related to the EarthR=
17;s
axis of rotation?

8.Where=
would
you have to look to see your zenith?Where on Earth would you have to be for the celestial equator to pass
through your zenith?Where on=
Earth
would you have to be for south celestial pole to be at your zenith?

9.How m=
any
degrees is the angle from the horizon to the zenith?Does your answer depend on what po=
int on
the horizon you choose?

10.Why
can’t a person in Antarctica use t=
he Big
Dipper to find the north direction?

11.Is t=
here any
place on Earth where you could see the north celestial pole on the northern
horizon?If so, where?Explain your answers.

12.How =
do the
stars appear to move over the course of the night as seen from the North
Pole?As seen from the
equator?Why are these two mo=
tions
different?

13.Usin=
g a
diagram, explain why the tilt of the Earth’s axis relative to the
Earth’s orbit causes the seasons as we orbit the Sun.

14.Give=
two
reasons why it’s warmer in summer than in winter.

15.What=
is the
ecliptic plane?What is the
ecliptic?

16.Why =
is the
ecliptic tilted with respect to the celestial equator?Does the Sun appear to move along =
the
ecliptic, the celestial equator, or neither?By about how many degrees does the=
Sun
appear to move on the celestial sphere each day?

17.Wher=
e on
Earth do you have to be in order to see the north celestial pole directly
overhead?What is the maximum
possible elevation of the Sun above the horizon at that location?On what date can this maximum elev=
ation
be observed?

18.What=
are the
vernal and autumnal equinoxes? What
are the summer and winter solstices?How are these four points related to the ecliptic and the celestial
equator?

19.At w=
hat
point on the horizon does the vernal equinox rise?Where on the horizon does it set?<=
span
style=3D'mso-spacerun:yes'> (Hint:See Figure 2-16.)

20.How =
does the
daily path of the Sun across the sky change with the seasons?Why does it change?

21.Wher=
e on
Earth do you have to be in order to see the Sun as the zenith?As seen from such location, will t=
he Sun
be at the zenith everyday?Explain.

22.What=
is
precession of the equinoxes?=
What
causes it?How long does it t=
ake
for the vernal equinox to move 1º along the ecliptic?

23.What=
is the
(fictitious) mean sun?What p=
ath
does it follow on the celestial sphere?&nb=
sp;
Why is it a better timekeeper than the actual Sun in the sky?

24.Why =
is it
convenient to divide the Earth into time zones?

25.Why =
is the
time given by a sundial not necessarily the same as the time on your
wristwatch?

26.What=
is the
difference between the sidereal year and the tropical year?Why are these two kinds of year sl=
ightly
different in length?Why are
calendars based on the tropical year?

27.When=
is the
next leap year?Was 2000 a le=
ap
year?Will 2100 be a leap yea=
r?

Advanced Questions

Questions prec=
eded by an
asterisk (*) involve topics discussed in the Boxes.

Problem-s=
olving
tips and tools

[Web link 2.4]&nb=
sp;
To help you visualize the heavens, it is worth taking the time to
become familiar with various types of star charts.These include the simple star =
charts
at the end of this book, the monthly star charts published in such
magazines as Sky & Telescop=
e and
Astronomy, and the more det=
ailed
maps of the heavens found in star atlases.

[Starry night]&nb=
sp;
One of the best ways to understand the sky and the motions is to=
use
the Starry Night EnthusiastT=
82;
computer program on the CD-ROM that accompanies certain printed copies =
of
this book.This easy-to-u=
se
program allows you to view the sky on any date and at any time, as seen
from any point on Earth, and to animate the sky to visualize its diurnal
and annual motions.

=
You
may also find it useful to examine a planisphere, a device consisting of
two rotatable disks.The =
bottom
disk shows all the stars in the sky (for particular latitude), and the =
top
one is opaque with a transparent oval window through which only some of=
the
stars can be seen.By rot=
ating
the top disk, you can immediately see which constellations are above the
horizon at any time of the year.A planisphere is a convenient tool to carry with you when you are
out observing the night sky.

28.On N=
ovember
1 at 8:30 P.M. you look toward the eastern horizon and see the bright star
Bellatrix (shown in Figure 2-2b)
rising.At approximately what=
time will
Bellatrix rise one week later, on November 8?

29.Figu=
re 2-4
shows the situation on September 21, when Cygnus is highest in the sky at 8=
:00
P.M. local time and Andromeda is highest in the sky at midnight.But as Figure 2-5 shows, on July 21
Cygnus is highest in the sky at midnight.&=
nbsp;
On July 21, at approximately what local time is Andromeda highest in=
the
sky?Explain your reasoning.<=
/p>

30.Figu=
re 2-5
shows which constellations are high in the sky (for observers in the northe=
rn
hemisphere) in the months of July, September, and November.From this figure, would you be abl=
e to
see Perseus at midnight on May 15?Draw a picture to justify your answer.

31.Figu=
re 2-6
shows the appearance of Polaris, the Little Dipper, and the Big Dipper at 11
P.M. (daylight savings time) on August 1.&=
nbsp;
Sketch how these objects would appear on this same date at (a) 8 P.M.
and (b) 2 A.M.Include the ho=
rizon
in your sketches, and indicate the north direction.

32.Figu=
re 2-6
shows the appearance of the sky near the North Star at 11 P.M. (day light
savings time) on August 1.Ex=
plain
why the sky has this same appearance at 1 A.M. on July 1 and at 9 P.M. on
September 1.

33.The
time-exposure photograph that opens this chapter shows the trails made by
individual stars, as the celestial sphere appears to rotate around the
Earth.(a) For approximately =
what
length of time was the camera shutter left open to take this photograph? (b) The stars in this photograph (=
taken
in Hawaii, at
roughly 20º north latitude) appear to rotate around one of the celesti=
al
poles.Which celestial pole is
it?As seen from this locatio=
n, do
the stars move clockwise or counterclockwise around this celestial pole? (c) If you were at 20º south
latitude, which celestial pole could you see?In which direction would you look =
to see
it?As seen from this locatio=
n, do
the stars move clockwise or counterclockwise around this celestial pole? =
p>

34.(a) =
Redraw
Figure 2-10 for an observer at the North Pole.(Hint:
The north celestial pole is directly above this observer.)(b) Redraw a Figure 2-10 for an ob=
server
at the equator.(Hint: The celestial equator passes
through this observer’s zenith.)&nbs=
p;
(c) Using Figure 2-10 and your drawings from (a) and (b), justify the
following rule, long used by navigators: The latitude of an observer in the
northern hemisphere is equal to the angle in the sky between that
observer’s horizon and the north celestial pole.(d) State the rule that correspond=
s to
(c) for an observer in the southern hemisphere.

35.The =
photograph
that opens this chapter was taken next to the Gemini North Observatory atop
Mauna Kea in Hawaii.The telescope is at longitude 155&=
ordm;
28’ 09” west and latitude 19º 49’ 26” north. (a) By making measurements on the
photograph, find the approximate angular width and angular height of the
photo.(b) How far (in degree=
s,
arcminutes, and arcseconds) from the south celestial pole can a star be and
still be circumpolar as seen from the Gemini North Observatory?

36.The =
Gemini
North Observatory shown in the photograph that opens this chapter is locate=
d in
Hawaii,
roughly 20º north of the equator.&nbs=
p;
Its near-twin, the Gemini South Observatory, is located roughly 30&o=
rdm;
south of the equator in Chile,
Why is it useful to have telescopes in both the northern and southern
hemisphere?

37.Is t=
here any
place on Earth where all the visible stars are circumpolar?If so, where?Is there any place on Earth where =
none
of the visible stars is circumpolar?If so, where?Explain =
your
answers.

38.The =
above
image of the Earth was made by the =
Galileo
spacecraft while en route to Jupiter.&=
nbsp;
South America is at the center of the image of Antarctica
is at the bottom of the image. (a)
In which month of the year was this image made?Explain your reasoning.(b) When this image was made. Was =
the
Earth relatively close to the Sun or relatively distant from the Sun?Explain your reasoning.

39.Figu=
re 2-16
shows the daily path of the Sun across the sky on March21, June 21, Septemb=
er
22, and December 21 for an observer at 35º north latitude.Sketch drawings of this kind for (=
a) an
observer at 35º south latitude; (b) an observer at the equator; and (c=
) an
observer at the North Pole.

40.Supp=
ose that
you live at a latitude of 40º N.What is the elevation (angle) of the Sun above the southern horizon =
at
noon (a) at the time of the vernal equinox?(b) At the time of the winter
solstice?Explain your
reasoning.Include a drawing =
as
part of your explanation.

41.In t=
he
northern hemisphere, houses are designed to have “southern
exposure,” that is, with the largest windows on the southern side of =
the
house.But in the southern
hemisphere houses are designed to have “northern exposure.”Why are houses designed this way a=
nd why
is there a difference between the hemispheres?

42.The =
city of Mumbai (formerly Bombay) in
India
is 19º north of the equator.On how many days of the year, if any, is the Sun at the zenith at mi=
dday
as seen from Mumbai? Explain your answer.

43.Anci=
ent
records show that 2000 years ago, the stars of the constellation Crux (the
Southern Cross) was visible in the southern sky from Greece.Today, however, these stars cannot=
be
seen from Greece.What accounts for this change?

44.The =
Great
Pyramid at Giza
has a tunnel that points toward the north celestial pole.At the time the pyramid was built,
around 2600 B.C., toward which star did it point?Toward which star does this same t=
unnel
point today?(See Figure 2-20=
.)

45.The =
photo on
the next page shows a statue of the Greek god Atlas.The globe that Atlas is holding
represents the celestial sphere, with depictions of the several important
constellations and the celestial equator.&=
nbsp;
Although the statue dates from around 150 A.D., it has been proposed
that the arrangement of constellations depicts the sky as it was mapped in =
an
early star atlas that dates from 129 B.C.&=
nbsp;
Explain the reasoning that could lead to such proposal.

46.Unli=
ke Western Europe, Imperial Russia did not use the rev=
ised
calendar instituted by Pope Gregory XIII.&=
nbsp;
Explain why the Russian Revolution, which started on November 7, 191=
7,
according to the modern calendar, is called “the October
revolution” in Russia.What was this date according to the
Russian calendar at the time?Explain.

*47.Wha=
t is the
right ascension of a star that is on the meridian at midnight at the time of
the autumnal equinox?Explain=
.

*48.The
coordinates on the celestial sphere of the summer solstice are R.A. =3D 6h
0m 0s, Decli. =3D +23º 27’.What are the right ascension and
declination of the winter solstice?Explain your answer.

*49.Bec=
ause 24
hours of right ascension takes you all the way around the celestial equator=
, 24h
=3D 360º, what is the angle in the sky (measured in degrees) between a=
star
with R.A. =3D 8h 0m 0s, Decl. =3D 0º =
o’
0” and a second star with R.A. =3D 11h 20m 0s,
Decl. =3D 0º 0’ 0”?Explain your answer.

*50.On a
certain night, the first star in Advanced Question 49 passes through the ze=
nith
at 12:30 A.M. local time.At =
what
time will eh second star pass through the zenith?Explain your answer.

*51.At =
local
noon on March 21, when the Sun is at the vernal equinox, a sidereal clock w=
ill
say that it is midnight.Expl=
ain
why.

*52.(a)=
What is
the sidereal time when the vernal equinox rises? (b) On what date is the
sidereal clock will say that it is midnight.Explain why.

*53.How=
would
the sidereal and solar days change (a) if the Earth’s rate of rotation
increased, (b) if the Earth’s rate of rotation decreased, and (c) if =
the
Earth’s rotation were retrograde (that is, if the Earth rotated about=
its
axis opposite to the direction in which it revolves about the Sun)?

Chapter 3 Questions____________________________<=
o:p>

Review Questions

=
(b) Acommon
misconception about the Moon’s phases is that they are caused by=
the
Earth’s shadow.Use
figure 3-2 to explain why this is not correct.

age of the Moon.This is the time that has elapsed since new moon phase.Thus, the age of a full moon =
is
half of a 29 ½-day synodic period, or approximately 15 days. Find the approximate age of (=
a) a
waxing crescent moon; (b) a third quarter moon; (c) a waning gibbous m=
oon.

If so, would the sequence of =
phases
be the same as those of the Moon as seen from Earth, or would the sequ=
ence
be reversed? Explain using Figure 3-2.

the same as the d=
ark
side of the moon?Explai=
n.

Explain.(b) Would you see the earth r=
ise
set, or would it always be in the same place in the sky?Explain using Figure 3-4

=

Which is longer? Why?

When wi=
ll the
moon next be in the direction of Gemini: on e sidereal month later, or=
one
synodic month later?Exp=
lain

How did
ancient astronomers use it to predict eclipses?

Advanced Questions

terminator.<=
span
style=3D'mso-spacerun:yes'> The terminator appears curved=
when
there is a crescent or gibbous moon, but appears straight when there i=
s a
first quarter or third quarter moon (see figure 3-2).Describe how you could use th=
ese
facts to explain to a friend why lunar phases cannot be caused by the
earth’s shadow falling on the moon.

At approximately what time do=
es the
moon cross the meridian if it is (a) a new moon; (b) a first quarter m=
oon;
(c) a full moon; (d) a third quarter moon? Explain your answers.

<=
/o:p>

Explain your answers.

What is the phase of the moon=
if
the moon is located at (a) the vernal equinox? (b) the summer solstice?
(c) the autumnal equinox? (d) the winter solstice? Explain your answer=
s. (Hint: Make a drawing showing =
the
relative positions of the sun, earth, and moon. Compare with figure 3-=
2.)

Apollo 8 spacecraft as they o=
rbited
the moon.A portion of t=
he
lunar surface is visible at the right-hand side of the photo. In this
photo, the earth is oriented with its north pole approximately at the
top.When this photo was
taken, was the moon waxing or waning as seen from Earth? Explain your
answer with a diagram.

what angle (in degrees) does =
the
moon move during a 12-hour night? Can you notice an angle of this size=
?

If the moon’s motion is assumed to be uniform and the
occultation was “central” (that is, center over center), f=
ind
the angular diameter of Jupiter. (Hint: Assume that Jupiter does not
appear to move against the background of stars during this brief 90-se=
cond
interval.You will need =
to
convert the moon’s angular speed from degrees per day to arcseco=
nds
per second.)

angle from the celestial
equator.Could the moon =
ever
appear at your zenith of you lived at (a) the equator; (b) the south p=
ole?
Explain your answers.

How many more sidereal months =
than
synodic months are there in a year? Explain

If the speed of the moon̵=
7;s
orbit around the earth were unchanged, would the length of the sidereal
month be the same, longer, or shorter than it is now? What about the
synodic month? Explain your answers.

Use this to explain why a glo=
w is
visible all around the horizon when you are viewing a solar eclipse du=
ring
totality (see figure 3-10a).

from the=
Earth
to the moon varies somewhat as the moon orbits the Earth, the distance
from the sun to the earth changes as the earth orbits the sun. The ear=
th
is closest to the sun at its p=
erihelion;
it is farthest from the sun at its aphelion.
In order for a total solar eclipse to have the maximum duration of
totality, should the earth be at perihelion or aphelion? Assume that t=
he
earth-moon distance is the same in both situations. As part of your
explanation, draw two pictures like figure 3-11, one with the earth
relatively far from the sun.

Chapter
4____________________________________

Review Questions

How
did the ancient Greeks explain why the sun and moon slowly change their
positions relative to the background stars?

In
what direction does a planet move relative to the stars when it is in
direct motion? When it is in retrograde motion? How do these compare w=
ith
the direction in which we se the sun move relative to the stars?

<=
/o:p>

(a)
In what direction does a planet move relative to the horizon over the
course of one night?(b)=
The
answer to (a) is the same whether the planet is in direct motion or
retrograde motion.What =
does
this tell you about the speed at which planets move on the celestial
sphere?

What
is an epicycle?How is it
important in Ptolemy’s explanation of the retrograde motions of =
the
planets?

What
is the significance of Occam’s razor as a tool for analyzing
theories?

How
did the models of Aristarchus and Copernicus explain the retrograde mo=
tion
of the planets?

How
did Copernicus determine that the orbits of Mercury and Venus must be
smaller than the Earth’s orbit? How did he determine that the or=
bits
of Mars, Jupiter and Saturn must be larger than the earth’s orbi=
t?

At
what configuration(for
example, superior conjunction, greatest eastern elongation, and so on)
would it be best to observe Mercury or Venus with an Earth-based
telescope? At what configuration would it be best to observe Mars,
Jupiter, or Saturn? Explain your answers.

Is
it ever possible to see Mercury at midnight? Explain your answer.

=

Which
planets can never be seen at opposition? Which planets can never be se=
en
at inferior conjunction? Explain your answer.

What
is the difference between the synodic period and the sidereal period o=
f a
planet?

What
is parallax? What did Tycho Brahe conclude from his attempt to measure=
the
parallax of a supernova and a comet?

What
observations did Tycho Brahe make in an attempt to test the heliocentr=
ic
model? What were his results explain why modern astronomers get differ=
ent
results.

What
are the foci of an ellipse? If the sun is at one focus of a planetR=
17;s
orbit, what is at the other focus?

What
are Kepler’s three laws? Why are they important?

<=
/li>

At
what point in a planet’s elliptical orbit does it move fastest? =
At
what point does it move slowest? At what point does it sweep out an ar=
ea
at the fastest rate?

A
line joining the sun and an asteroid is found to sweep out an area of =
6.3
AU2 during 2010. How much area is swept out during 2011? Over a period=
of
5 years?

The
orbit if a spacecraft about the sun has a perihelion distance of 0.1 AU
and an aphelion distance of 0.4 AU. What is the semi major axis of the
spacecrafts orbit? What is its orbital period?

A
comet with a period of 125 years moves in a highly elongated orbit abo=
ut
the sun.At perihelion, =
the
comet comes very close to the sun’s surface. What is the
comet’s average distance from the sun? What is the farthest it c=
an
get from the sun?

What
observations did Galileo make that reinforced the heliocentric model? =
Why
did these observations contradict the older model of Ptolemy why could
these observations no have been made before Galileo’s time?

=

Why
does Venus have its largest angular diameter when it is new and its
smallest angular diameter when it is full?

What
re Newton’s
3 laws? Give an everyday example of each law.

How
much force do you have to exert on a 3-kg brick to give it an accelera=
tion
of 2 m/s2? If you double this force, what is the brick’s
acceleration? Explain.

What
is the difference between weight and mass?

What
is your weight in pounds and in Newton’s?
What isyour mass in
kilograms?

Suppose
that the earth were moved to a distance of 3.0 AU from the sun. how mu=
ch
stronger/weaker would the sun’s gravitational pull of its gravit=
y?
Explain.

How
far would you have to go from Earth to be completely beyond the pull of
its gravity? Explain.

What
are conic sections? In what way are they related to the orbits of plan=
ets
in the solar system?

Why
was the discovery of Neptune an important confirmation of Newton’=
s law of
universal gravitation?

What
is a tidal force? How do tidal forces produce tides in the Earth’=
;s
oceans?

What
is the difference between spring tides and neap tides?

<=
/li>

Advanced Questions

Figure
4-2 shows the retrograde motion of Mars as seen from Erath. Sketch a
similar figure that shows how earth would appear to move against the
background of stars during this same time period as seen by an observe=
r on
Mars.

The
synodic period of Mercury (an inferior planet) is 115.88 days. Calcula=
te
its sidereal period in days.

Table
4-1 shows that the synodic period is greater than the sidereal period =
for
Mercury, but the synodic period is less than the sidereal period for
Jupiter. Draw diagrams like the one in Box 4-1 to explainwhy this is so.

A
general rule for superior planets is that the greater the average dist=
ance
from the planet to the sun, the more frequently that planet will be at
opposition. Explain how this rule comes about.

In
2006, Mercury was at greatest western elongation on April 8, August 7,
November 25. It was at greatest eastern elongation on February 24, June
20, and October 17. Does Mercury take longer to go from eastern to wes=
tern
elongation, or vice versa? Explain why, using figure 4-6.

=
u>

Explain
why the semimajor axis of a planet’s orbit is equal to the avera=
ge
of the distance from the sun to the planet at perihelion (the periheli=
on
distance) and the distance from the sun to the planet at aphelion (the
aphelion distance).

A
certain comet is 2 AU from the sun at perihelion and 16 AU from the su=
n at
aphelion. (a) Find the semimajor axis of the comet’s orbit. (b) =
Find
the sidereal period of the orbit.

A
comet orbits the sun with a sidereal period of 64.0 years. (a) Find the
semimajor axis of the orbit. (b) At aphelion, the comet is 31.5 AU from
the sun. How far is it from the sun at perihelion?

One
trajectory that can be used to send spacecraft from the earth to Mars =
is
an elliptical orbit that has the sun at one focus, its perihelion at t=
he
earth, and its aphelion at Mars. The spacecraft if launched form Earth=
and
coasts along this ellipse until it reaches Mars, when a rocket is fire=
d to
either put the spacecraft into orbit around Mars or cause to land on M=
ars.
(a) Find the semimajor axis of the ellipse. (Hint: Draw a picture show=
ing
the sun and the orbits of the earth, Mars, and the spacecraft. Treat t=
he
orbits of the earth and Mars as circle.) (b) Calculate how long (in da=
ys)
such a one-way trip to Mars would take.

The
mass of the moon is 7.35 X 10 to the power of22 kg. The average distance f=
rom the
center of the moon to the center of the Earth is 384,400 km. What is t=
he
size of the gravitational force that the Earth exerts on the moon? Wha=
t is
the size of the gravitational force that the moon exerts on the Earth?=
How
do your answers compare with the force between the sun and the earth
calculated in the text?

The
mass of Saturn is approximately 100 times that of earth, and the semim=
ajor
axis of Saturn’s orbit is approximately 10 AU. To this
approximation, how does the gravitational force that the sun exerts on
Saturn compare to the gravitational force that the sun exerts on the
earth? How do the accelerations of Saturn and the earth compare?

<=
/o:p>

Suppose
that you traveled to a planet with4 times the mass and 4 times the
diameter of the Earth. Would you weigh more or less on that planet tha=
n on
earth? By what factor?

On
earth, a 50-kg astronaut weighs 490 Newton’s.
What would she weigh if she landed on Jupiter’s moon Callisto? W=
hat
fraction is this of her weight on earth? See appendix 3 for relevant d=
ata
about Callisto.

Imagine
a planet like the earth orbiting a star with 4 times the mass of the s=
un.
if the semimajor axis of the planet’s orbit is 1AU, what would be
the planet’s sidereal period? (Hint: Use <=
st1:place
w:st=3D"on">Newton’s form of Kepler̵=
7;s
third law. Compared with the case of the Earth orbiting the sun, by wh=
at
factor has the quantity m1+m2 changed? Has a changed? By what factor must p2 change?)

<=
/li>

A
satellite is said to be in a “geosynchronous” orbit if it
appears always to remain over the exact same spot on the rotating Eart=
h.
(a) What is the period of this orbit? (b) At what distance from the ce=
nter
of the earth must such a satellite be placed into orbit? (Hint: Use Newton’=
;s form
of Kepler’s third law.) (c) Explain why the orbit must be in the
plane of the earth’s equator.

Figure
4-21 shows the lunar module Ea=
gle
in orbit around the moon after completing the first successful lunar
landing in July 1969.(T=
he
photograph was taken from the command module Columbia
, in which the astronauts returned to Earth.) The spacecraft orbited 1=
11
km above the surface of the Moon. Calculate the period of the spacecra=
fts
orbit. See appendix 3 for relevant data about the moon.

=

In
box 4-4<=
/st1:address>
we analyze the orbit of Jupiter’s moon Io. Look up information a=
bout
the orbits of Jupiter’s three other large moons (Europa, Ganymed=
e,
and Callisto) in appendix 3. Demonstrate that these data are in agreem=
ent
with Newton=
st1:City>’s
form of Kepler’s third law.

Suppose
a newly discovered asteroid is in a circular orbit with synodic period=
of
1.25 years. The asteroid lies between the orbits of mars and Jupiter. =
(a)
Find the sidereal period of the orbit. (b) Find the distance from the
asteroid to the Sun.

The
average distance from the moon to the center of the earth is 384,400 k=
m,
and the diameter of the earth is 12,756 km. Calculate the gravitational
force that the moon exerts (a) on a 1-kg rock at the point on the
earth’s surface fathers from the moon . (c) Find the difference
between the two forces you calculated in parts (a) and (b). This
difference is the tidal force pulling these two rocks away from each
other, like the 1-ball and 3—ball in figure 4-24. Explain why ti=
dal
forces cause only a very small deformation of the earth.

Chapter 5___________________________________

=
o:p>

REVIEW QUESTI=
ONS:

1.Wh=
en
Jupiter is undergoing retrograde motion as seen from Earth, would you expect
the eclipses of Jupiter’s moons to occur several minutes early, sever=
al
minutes late, or neither? Explain.

2.Ap=
proximately
how many times around the earth could a beam of light travel in one second?=

3.Ho=
w long
does it take light to travel from the Sun to the Earth, a distance of 1.50 =
x 108
Km?

4.Ho=
w did Newton show that a=
prism
breaks white light into its component colors, but does not add any color to=
the
light?

6.Wh=
at is
meant by the frequency of light?How is frequency related to wavelength?

7.A =
cellular
phone is actually a radio transmitter and receiver.You receive an incoming call in th=
e form
of a radio wave of frequency 880.65 Mhz.&n=
bsp;
What is the wavelength (in meters) of this wave?

8.A =
light
source emits infrared radiation at a wavelength of 1150 nm.What is the frequency of this radi=
ation?

9.(a=
) What
is a blackbody? (b) In what way is a blackbody black? (c ) If a blackbody is
black, how can it emit light? (d) If you were to shine a flashlight beam on=
a
perfect blackbody, what would happen to the light?

10.W=
hy do
astronomers find if convenient to sue the Kelvin temperature scale in their
work rather than the Celsius of Fahrenheit scale?

11.E=
xplain
why astronomers are interested in blackbody radiation.

12.U=
sing
Wien’s law and the Stefan-Boltzmann law, explain the color and intens=
ity
changes that are observed as the temperature of a hot, glowing object
increases.

13.I=
f you
double the Kelvin temperature of a hot piece of steel, ho much more energy =
will
it radiate per second?

14.T=
he
bright star Bellatrix in the constellation Orion has a surface temperature =
of
21,500 K.What is its wavelen=
gth of
maximum emission in nanometers?What color is this star?

15.T=
he
bright star Antares in the constellation Scorpius (the Scorpion) emit’=
;s
the greatest intensity of radiation at a wavelength of 853 nm.What is the surface temperature of
Antares?What color is this s=
tar?

16.(=
a)
Describe an experiment in which light behaves like a wave.(b) Describe an experiment in which
light behaves like a particle.

17.H=
ow is
the energy of a photon related to its wavelength?What kind of photons carry the most
energy?What kind of photons =
carry
the least energy?

18.T=
o emit
the same amount of light energy per second, which must emit more photons per
second: a source of red light, or a source of blue light?Explain.

19.E=
xplain
how much we know that atom have massive, compact nuclei.

20.(=
a)
Describe the spectrum of hydrogen at visible wavelengths.(b) Explain how Bohr’s model=
of
the atom accounts for the Balmer lines.

21.W=
hy do
different elements display different patterns of lines in their spectra?

22.W=
hat is
the Doppler effect?Why is it
important to astronomers?

23.I=
f you
see a blue star, what does its color tell you about how the star is moving
through space?Explain your a=
nswer.

ADVANCED QUES=
TIONS:

=
o:p>

PROBLEM-SOLVI=
NG TIPS
AND TOOLS:

You can find f=
ormulas
in Box 5-1 for
converting between temperature scales.&nbs=
p;
Box 5-2
discusses how a star’s radius, luminosity, and surface temperature are
related.Box
5-3 shows how to sure Planck’s law to
calculate the energy of a photon.To learn how to do calculations using the Doppler effect, see Box
5-6.

24.Y=
our
normal body temperature is 98.6F.What kind of radiation do you predominantly emit?At what wavelength (in nm) do you =
emit
the most radiation?

25.W=
hat is
the temperature of the Sun’s surface in degrees Fahrenheit?

26.W=
hat
wavelength of electromagnetic radiation is emitted with greatest intensity =
by
this book?To what region of =
the
electromagnetic spectrum does this wavelength correspond?

27.B=
lack
holes are objects who’s gravity is so strong that not even an object
moving at the speed of light can escape from their surface.Hence, black holes do not themselv=
es
emit light.Be it is possible=
to
detect radiation from material falling toward a black hole.Calculations suggest that as this =
matter
falls, it is compressed and heated to temperatures around 106
K.calculate the wavelength of
maximum emissions for this temperature.&nb=
sp;
In what part of the electromagnetic spectrum does this wavelength li=
e?

*28.=
Use the
value of the solar constant given in Box 5-2=
st1:Street>
and the distance from the Earth to the Sun to calculate the luminosity of t=
he
Sun.

*29.=
The star
Alpha Lupi (the brightest star in the constellation Lupus, the Wolf) has a
surface temperature of 21,600 K.How much more energy is emitted each second from each square meter of
the surface of Alpha Lupi than from each square meter of the Sun’s
surface?

*30.=
Jupiter’s
moon Io has an active volcano named Pele whose temperature can be as high as
320 C. (a) What is the wavelength of the maximum emission for the volcano at
this temperature?In what par=
t of
the electromagnetic spectrum is this?(b) The average temperature of Io’s surface is -150 C.Compared with a square meter of su=
rface
temperature, how much more energy is emitted per second from each square me=
ter
of Pele’s surface?

*31.=
The
bright star Sirius in the constellation of Canis Major (the Large Dog) has a
radius of 1.67 R.and a lumin=
osity
of 25L. .(a) Use this inform=
ation
to calculate the energy flux at the surface of Sirius.(b) Use your answer in part (a) to
calculate the surface temperature of Sirius.How does your answer compare to the
value given in Box 5-2?

32.I=
n Figure
5-13you can see two distinct=
dark
lines at the boundary between the orange and yellow parts of the Sun’s
spectrum (in the center of the third colored band from the top of the
figure).The wavelengths of t=
hese
dark lines are 588.99 and 589.59 nm.What do you conclude from this about the chemical composition of the
Sun’s atmosphere? (Hint: See Section 5-6)

33.I=
nstruments
on board balloons and spacecraft detect 511-keV photons coming from the
direction of the center of our Galaxy.&nbs=
p;
(The prefix k means kilo, or thousand, so 1keV =3D 103
eV.)What is the wavelength of
these photons?To what part o=
f the
electromagnetic spectrum do these photons belong?

34.(=
a)
Calculate the wavelengths of P (P-delta), the fourth wavelength in the Pach=
en
series.(b) Draw a schematic
diagram of the hydrogen atom and indicate the electron transition that gives
rise to this spectral line.(=
c ) In
what part of the electromagnetic spectrum does this wavelength lie.

35.(=
a)
Calculate the wavelength for H (H-eta), the spectral line for an electron
transition between the n=3D7 and the n=3D2 orbits of hydrogen.(b) In what part of the electromag=
netic
spectrum does this wavelength lie?Use this to explain why figure 5-2 is labeled RIVUXG.

36.C=
ertain
interstellar clouds contain a very cold, very thin gas of hydrogen atoms. Ultraviolet radiation with any
wavelength shorter than 91.2 nm cannot bass through this gas; instead, it is
absorbed.Explain why.

=
o:p>

37.(=
a) Can a
hydrogen atom in the ground stat absorb an H-alpha photon?Explain why or why not.(b) Can a hydrogen atom in the n=
=3D2 state
absorb a Lyman-alpha photon? Explain why or why not.

38.An
imaginary atom has just 3 energy levels: 0 eV, 1 eV, and 3eV.Draw an energy-level diagram for t=
his
atom.Show all possible trans=
itions
between these energy levels.=
For
each transition, determine the photon energy and the photon wavelength.Which transitions involve the emis=
sion
of absorption of visible light?

39.T=
he star
cluster NGC 346 and nebula shown in Figure 5-18 are located within the Small
Magellanic Cloud (SMC), a small galaxy that orbits our Milky Way Galaxy. The SMC and the stars and gas with=
in it
are moving away from us at 158 km/s.at which wavelength does the red H-alpha line of hydrogen (which cau=
ses
the color of the nebula) appear in the nebula’s spectrum?

<=
/u>

40.T=
he
wavelength of H-beta in the spectrum of the star Megrez in the Big Dipper (=
part
of the constellation Ursa Major, the Great Bear) is 486.112 nm.Laboratory measurements demonstrat=
e that
the normal wavelength of this spectral line is 486.133 nm. Is the star coming toward us or mov=
ing
away from us?At what speed?<=
o:p>

41.Y=
ou are
given a traffic tick for going through a red light(wavelength 700 nm).You tell the police officer that b=
ecause
you were approaching the light, the Doppler effect caused a blue shift that
made the light appear green (wavelength 500nm).How fast would you have to be goin=
g for
this to be true?Would the sp=
eeding
ticket be justified?Explain.=

2.Ex=
plain
why a flat piece of glass does not bring light to a focus while a curved pi=
ece
of glass can.

3.Ex=
plain
why the light rays that enter a telescope from an astronomical object are
essentially parallel.

4.Wi=
th the
aid of a diagram, describe a refracting telescope.Which dimensions of the telescope
determine its light-gathering power?Which dimensions determine the magnification?

5.Wh=
at is
the purpose of the telescope eyepiece?&nbs=
p;
What aspect of the eyepiece determines the magnification of the
image?In what circumstances =
would
the eyepiece not be used?

6.Do most
professional astronomers actually look through their telescopes?Why or why not?

7.Qu=
ite
often advertisements appear for telescopes that extol their magnifying
power.Is this a good criteri=
on for
evaluating telescopes?Explai=
n your
answer.

8.Wh=
at is
chromatic aberration?For what
kinds of telescopes does it occur? <=
/span>How
can it be corrected?

9.With =
the
aid of a diagram, describe a reflecting telescope.Describe four different ways in wh=
ich an
astronomer can access the focal plane.

10.E=
xplain
some of the disadvantages of refracting telescopes compared to reflecting
telescopes.

11.W=
hat kind
of telescope would you use if you wanted to take a color photograph entirely
free of chromatic aberration?Explain your answer.

12.E=
xplain
why a Cassegrain reflector can be substantially shorter than a refractor of=
the
same focal length.

13.N=
o major
observatory has a Newtonian reflector as its primary instrument, whereas
Newtonian reflectors are extremely popular among amateur astronomers.Explain why this is so.

14.W=
hat is
spherical aberration?How can=
it be
corrected?

15.W=
hat is
diffraction?Why does it limi=
t the
angular resolution of a telescope?What other p physical phenomenon is often a more important restricti=
on
on angular resolution?

16.W=
hat is
active optics?What is adapti=
ve
optics?Why are then useful?<=
span
style=3D'mso-spacerun:yes'> Would either of these be a good fe=
ature
to include on a telescope to be placed in orbit?

17.E=
xplain
why combining the light from two or more optical telescopes can give
dramatically improved angular resolution.

18.W=
hat is
light pollution?What effects=
does
it have on the operation of telescopes?&nb=
sp;
What can be done to minimize these effects?

19.W=
hat is a
charge-coupled device (CCD)?=
What
have CCDs replace photographic film for recording astronomical images?

=

20.W=
hat is a
spectrograph?Why do many
astronomers regard it as the most important device that can be attached to a
telescope?

21.What=
are
the advantages of using a diffraction grating rather than a prism n a
spectrograph?

22.C=
ompare
an optical reflecting telescope and a radio telescope.What do they have in common?How are they different?

=

23.W=
hy can
radio astronomers make observations at any time during the day, whereas opt=
ical
astronomers are mostly limited to observing at night? (Hint: Does your radio
work any better or worse in the daytime than at night?)

24.W=
hy are
radio telescopes so large?Wh=
at
does a single radio telescope have poorer angular resolution than a large
optical telescope?How can the
resolution be improved by making simultaneous observations with several rad=
io
telescopes?

25.W=
hat are
the optical window and the radio window?&n=
bsp;
Why isn’t there an X-ray window or an ultraviolet window?

=

26.W=
hy is it
necessary to keep an infrared telescope at a very low temperature?

27.H=
ow are the
images made by an X-ray telescope different from those made by a medical X-=
ray
machine?

28.W=
hy must
astronomers use satellites and Earth-orbiting observatories to study the
heavens at X-ray and gamma-ray wavelengths?

ADVANCED QUES=
TIONS:

PROBLEM-SOLVI=
NG TIPS
AND TOOLS:

You may find i=
t useful
to review the small-angle formula discussed in Box
1-1.The area of a circle is proportional to the square of its diameter.<=
span
style=3D'mso-spacerun:yes'> Data on the planets can be found i=
n the
appendices at the end of this book.Section 5-2 discusses the relationship between frequency and
wavelength.Box
6-1 gives examples of how to calculate magnify=
ing
power and light-gathering power.

29.S=
how by
means of a diagram why the image formed by a simple refracting telescope is
upside down.

30.O=
rdinary
photographs made with a telephoto lens objects appear close.How does the focal length of a tel=
ephoto
lens compare with that of a normal lens?&n=
bsp;
Explain your reasoning.

31.T=
he
observing cage in which an astronomer can sit at the prime focus of the 5-m
telescope on Palomar<=
/st1:PlaceName>
Mountain
is about 1 m in diameter.Cal=
culate
what fraction of the incoming starlight is blocked by the cage.

<=
/u>

32.(=
a)
Compare the light-gathering power of the Keck I 10.0-m telescope with that =
of
the Hubble Space Telescope (HST), which has a 2.4-m objective mirror.(b) What advantages does Keck I ha=
ve
over HST?What advantages doe=
s HST
have over Keck I?

33.S=
uppose
your Newtonian reflector has an objective mirror 20 cm (8 in.) in diameter =
with
a focal length of 2m.What
magnification do you get with eyepieces who focal lengths are (a) 9 mm, (b)=
20
mm, and (c ) 55 mm?(d) What =
is the
telescope’s diffraction-limited angular resolution when used with ora=
nge
light of wavelength 600 nm? (e) Would it be possible to achieve this angular
resolution if you took the telescope to the summit of Mauna Kea?Why or why not?

34.S=
everal
groups of astronomers are making plans for large ground-based telescopes. (a) What would be the
diffraction-limited angular resolution of a telescope with a 40-meter objec=
tive
mirror?Assume that yellow li=
ght
with wavelength 550 nm is used. (b)
Suppose this telescope is placed atop Mauna Kea.How will the actual angular resolu=
tion
of the telescope compare to that of the 10-meter Keck I telescope?Assume that adaptive optics is not=
used.

35.T=
he
Hobby-Eberly Telescope (HET) at the McDonald Observatory in Texas
has a spherical mirror, which is least expensive to shape to grind.Consequently, the telescope has
spherical aberration.Explain=
why
this doesn’t affect the usefulness of HET for spectroscopy.(The telescope is not used for ima=
ging.)

36.T=
he four
largest moons of Jupiter are roughly the same size as our Moon and are about
628 million (6.28 x 108) kilometers from Earth at opposition. What is the size in kilometers of =
the
smallest surface features that the Hubble Space Telescope (resolution of 0.1
arcsec) can detect.How does =
this
compare with the smallest features that can be seen on the moon with the
unaided human eye (resolution 1 archmin)?

37.T=
he
Hubble Space Telescope (HST) has been used to observe the galaxy M100, some=
70
million light-years from Earth. (a) If the angular resolution of the HST im=
age
is 0.1 arcsec, what is the diameter in light-years of the smallest detail t=
hat
can be discerned in the image? (b) At what distance would a U.S. dime (diam=
eter
1.8 cm) have an angular size of 0.1 arcsec? Give your answer in diameters.<=
o:p>

38.A=
t its
closest to Earth, Pluto is 28.6 AU from Earth.Can the Hubble Space Telescope
distinguish any features on Pluto?Justify your answer using calculation.

39.T=
he Institute<=
/st1:PlaceType>
of Space
and Astronautically Science in Japan
proposes to place a radio telescope into an even higher orbit than the HALCA
telescope.Using this telesco=
pe in
concert with ground-based radio-telescopes, baselines as long as 25,000 km =
may
be obtainable.Astronomers wa=
nt to
use this combination to study radio emissions at a frequency of 43 Ghz from=
the
molecule silicon monoxide, which is fund in the interstellar clouds from wh=
ich
stars from. (1GHZ =3D 1 gigahertz =3D 109 Hz) (a) What is the wa=
velength
of this emission? (b) Taking the baseline to be the effective diameter of t=
his
radio-telescope array, what angular resolution can be achieved?

<=
/u>

40.T=
he
mission of the Submillimeter Wave Astronomy Satellite (SWAS), launched in 1=
998,
was to investigate interstellar clouds within which stars form.One of the frequencies at wh=
ich it
observed these clouds is 557 GHz (1GHZ =3D 1 gigahertz =3D 109 H=
z),
characteristic of the emission from interstellar water molecules.(a) What is the wave length (in me=
ters)
of this emission?In what par=
t of
the electromagnetic spectrum is this? (b) Why was it necessary to use at
satellite for these observations? =
span>(c
) SWAS had an angular resolution of 4arcminutes.What was the diameter of its prima=
ry
mirror?

41.T=
o search
for ionized oxygen gas surrounding our Milky Way Galaxy, astronomers aimed =
the
ultraviolet telescope of the FUSE spacecraft at a distant galaxy far beyond=
the
Milky Way.The then looked fo=
r an
ultraviolet spectral line of ionized oxygen in that galaxy’s
spectrum.Were they looking f=
or an
emission line or an absorption line?Explain.

42.A
sufficiently thick interstellar cloud of cool gas can absorb low-energy X r=
ays
but is transparent to high-energy X rays and gamma rays.Explain why both part b and part d=
of
Figure 6-32 reveal the presence of cool gas in the Milky Way.Could you infer the presence of th=
is gas
from the visible-light image in Figure 6-32a?Explain.

Chapter 7 ___________________________________

Review Questi=
ons

1. Do all =
the
planets orbit the Sun in the same direction? Are all of the orbits circular=
?

2. What ar=
e the
characteristics of a terrestrial planet?

3. What ar=
e the
characteristics of a Jovian planet?

4. What is=
meant
by the average density of a planet? What does the average density of a plan=
et
tell us?

5. In What=
ways
are the largest satellites similar to the terrestrial planets? In what ways=
are
they different? Which satellites are the largest?

6. The abs=
orption
lines in the spectrum of a planet or satellite do not necessarily indicate =
the
composition of the planet or satellite’s atmosphere. Why not?

7. What ar=
e the
differences in chemical composition between the terrestrial and Jovian plan=
ets?

8. Why are
hydrogen and helium abundant in the atmospheres of the Jovian planets but
present in only small amounts in the Earth’s atmosphere?

=
u>

9. What is=
an
asteroid? What is a trans-Neptunian object? In what ways are these minor
members of the solar system like or unlike the planets?

<=
/p>

10. What a=
re the
asteroid belt, the Kuiper belt, and the Oort cloud? Where are they located?=
How
do the objects found in these three regions compare?

11. In wha=
t ways
in Pluto similar to a terrestrial planet? In what ways is it different?

12. What i=
s the
connection between comets and the Kuiper belt? Between comets and the Oort
Cloud?

13. What i=
s one
piece of evidence that impact craters are actually caused by impacts?

<=
/o:p>

14. What i=
s the
relationship between the extent to which a planet or satellite is cratered =
and
the amount of geologic activity on that planet or satellite?

15. How do=
we know
that the surface of Venus is older than the Earth’s surface but young=
er
than the Moon’s surface?

16. Why do=
smaller
worlds retain less of their internal heat?

17. How do=
es the
size of a terrestrial planet influence the amount of cratering on the
planet’s surface?

18. How is=
the
magnetic field of a planet different from that of a bar magnet? Why is a la=
rge
planet more likely to have a magnetic field than a small planet?

=

19. Could =
you use
a compass to find your way around Venus? Why or Why not?

=

20. If Mar=
s has no
planetwide magnetic field, why does it have magnetized regions on its surfa=
ce?

21. What i=
s liquid
metallic hydrogen? Why is it found only in the interiors of certain planets=
?

Advanced Q=
uestions

22. Mars h=
as two
small satellites, Phobos and Deimos. Phobos circles Mars once every 0.31891=
day
at an average altitude of 5980 km above the planet’s surface. The dia=
meter
of Mars is 6794 km. Using this information, calculate the mass and average
density of Mars.

23. Figure=
7-3
shows the spectrum of Saturn’s largest satellite, Titan. Can you thin=
k of
a way that astronomers can tell which absorption lines are due to TitanR=
17;s
atmosphere and which are due to the atmospheres of the Sun and Earth? Expla=
in.

*24. (a) F=
ind the
mass of hypothetical spherical asteroid 2 km in diameter and composed of ro=
ck
with average density 2500 kg/m (cubed). (b) Find the speed required to esca=
pe
from the surface of this asteroid. (c) A typical jogging speed is 3 m/s. Wh=
at
would you happen to an astronaut who decided to go for a jog on this astero=
id?

*25. The
hypothetical asteroid described in Question 24 strikes the Earth with a spe=
ed
of 25 km/s. (a) What is the kinetic energy of the asteroid at the moment of
impact? (b) How does this energy compare with that released by a 20-kiloton
nuclear weapon, like the device that destroyed Hiroshima, Japan,
on August 6, 1945? (Hint: 1 kiloton of TNT releases 4.2 X 10 (to the 12) jo=
ules
of energy.)

*26. Suppo=
se a
spacecraft landed on Jupiter’s moon Europa (see Table 7-2), which mov=
es
around Jupiter in an orbit of radius 670,900 km. After collecting samples f=
rom
the satellite’s surface, the spacecraft prepares to return to Earth. =
(a)
Calculate the escape speed from Europa. (b) Calculate the escape speed from
Jupiter at the distance of Europa’s orbit. (c) In order to begin its
homeward journey, the spacecraft must leave Europa with a speed greater than
either your answer to (a) or your answer to (b). Explain why.

=
u>

*27. A hyd=
rogen
atom has a mass of 1.673 X 10 (to the negative 27) kg, and the temperature =
of
the Sun’s surface is 5800 K. What is the average speed of hydrogen at=
oms
at the Sun’s surface?

*28. the
Sun’s mass is 1.989 X 10 (to the 30) kg, and its radius is 6.98 X 10 =
(to
the 8) m. (a) Calculate the escape speed from the Sun’s surface. (b)
Using your answer to Question 27, explain why the Sun has lost very little
hydrogen over its entire 4.56-billion-year history.

*29.
Saturn’s satellites Titan has an appreciable atmosphere, yet
Jupiter’s satellite Ganymede – which is about the same size and
mass as Titan – has no atmosphere. Explain why there is a difference.=

30. The di=
stance
from the asteroid 433 Eros (Figure 7-7) to the Sun varies between 1.13 and =
1.78
AU. (a) Find the period of Eros’s orbit. (b) Does Eros lie in the
asteroid belt? How can you tell?

31. Imagin=
e a
trans-Neptunian object with roughly the same mass as Earth but located 50 AU
from the Sun. (a) What do you think this object would be made of? Explain y=
our
reasoning. (b) On the basis of this speculation, assume a reasonable density
for this object and calculate its diameter. How many times bigger or smaller
than Earth would it be?

32. Consid=
er a
hypothetical trans-Neptunian object located 100 AU from the Sun. (a) What w=
ould
be the orbital period (in years) of this object? (b) There are 360 degrees =
in a
circle, and 60 arcminutes in a degree. How long would it take this object to
move 1 arcminute across the sky? (c) Trans-Neptunian objects are discovered=
by
looking for “stars: that move on the celestial sphere. Use your answer
from part (b) to explain why these discoveries require patience. (d)
Discovering trans-Neptunian objects also requires large telescopes equipped
with sensitive detectors. Explain why.

33. The su=
rfaces
of Mercury, the Moon, and Mars are riddled with craters formed by the impac=
t of
space debris. Many of these craters are billions of y ears old. By contrast,
there are only a few conspicuous craters on the Earth’s surface, and
these are generally less than 500 million years old. What do you suppose
explains the difference?

34. During=
the
period of most intense bombardment by space debris, a new 1-km-radius crater
formed somewhere on the Moon about once per century. During this same perio=
d,
what was the probability that such a crater would be created within 1 km of=
a
certain location on the Moon during a 100-yhear period? During a 10 (to the=
6)-
year period? (Hint: If you drop a coin onto a checkerboard, the probability
that the coin will land on any particular one of the board’s 64 squar=
es
is 1/64.)

35. When a=
n impact
crater is formed, material (called ejecta) is sprayed outward from the impa=
ct.
(The accompanying photograph of the Moon shows lighted-colored ejecta exten=
ding
outward from the crater Copernicus.) While ejecta are found surrounding the
craters on Mercury, they do not extend as far from the craters as do ejecta=
on
the Moon. Explain why, using the difference in surface gravity between the =
Moon
(surface gravity =3D0.17 that on Earth) and Mercury (surface gravity =3D 0.=
38 that
on Earth).

36. Mercury
rotates once on its axis every 58.646 days, compared to 1 day for the Earth.
Use this information to argue why Mercury’s magnetic field should be =
much
smaller than the Earth’s.

37. Suppos=
e Mars
Global Surveyor had discovered magnetized regions in the lowlands of Mars. =
How
would this discovery have affected our understanding of the evolution of the
Martian interior?

38. Liquid=
metallic
hydrogen is the source of the magnetic fields of Jupiter and Saturn. Explain
why liquid metallic hydrogen cannot be the source of the Earth’s magn=
etic
field.

Chapter 8__________________________________

=

Review Questi=
ons

1. Describ=
e three properties
of the solar system that are thought to be a result of how the solar system
formed.

2. The gra=
phite in
your pencil is a form of carbon. Where were these carbon atoms formed?

=

3. What is=
the
interstellar medium? How does it become enriched over time with heavy eleme=
nts?

4. What is=
the
evidence that other stars existed before our Sun was formed?

5. Why are
terrestrial planets smaller than Jovian planets?

6. How do
radioactive elements make it possible to determine the age of the solar sys=
tem?
What are the oldest objects that have been found in the solar system?

<=
/o:p>

7. What is=
the
tidal hypothesis? What aspect of the solar system was it designed to explai=
n?
Why was this hypothesis rejected?

8. What is=
the
nebular hypothesis? Why is this hypothesis accepted?

9. What wa=
s the
protosun? What caused it to shine? Into what did it evolve?

<=
/b>

10. Why is=
it
thought that a disk appeared in the solar nebula?

11. What a=
re
proplyds? What do they tell us about the plausibility of our model of the s=
olar
system’s origin?

12. What i=
s meant
by a substance’s condensation temperature? What role did condensation
temperatures play in the formation of the planets?

13. What i=
s a
planetesimal? How did planetesimals give rise to the terrestrial planets? <=
o:p>

14. (a) Wh=
at is
meant by accretion? (b) Why are the terrestrial planets denser at their cen=
ters
than at their surfaces?

15. If hyd=
rogen
and helium account for 98% of the mass of all the atoms in the universe, why
aren’t the Earth and Moon composed primarily of these two gasses?

16. What i=
s a
chondrule? How do we know they were not formed by the ambient heat of the s=
olar
nebula?

17. Why di=
d the
terrestrial planets form close to the Sun while the Jovian planets formed f=
ar
from the Sun?

18. What a=
re the
competing models of how the Jovian planets formed?

19. Explai=
n how
our current understanding of the formation of the solar system can account =
for
the following characteristics of the solar system: (a) All planetary orbits=
lie
in nearly the same plane. (b) All planetary orbits are nearly circular. (c)=
The
planets orbit the Sun in the same direction in which the Sun itself rotates=
.

20. Why is=
the
combined mass of all the asteroids so small? Why is the combined mass of all
trans-Neptunian objects so much greater than that for the asteroids?

=
o:p>

21. Explai=
n why
most of the satellites of Jupiter orbit that planet in the same direction t=
hat
Jupiter rotates.

22. What i=
s the
radial velocity method used to detect planets orbiting other stars? Why is =
it
difficult to use this method to detect planets like Earth?

=
b>

23. Summar=
ize the
differences between the planets of our solar system and those found orbiting
other stars.

24. Is the=
re
evidence that planets have fallen into their parent stars? Explain.

25. What d=
oes it
mean for a planet to transit a star? What can we learn from such events?

26. What is
microlensing? How does it enable astronomers to discover extrasolar planets=
?

27. A 1999=
news
story about the discovery of three planets orbiting the star Upsilon Androm=
edae
(“Ups And” in Figure 8-17) stated that “the newly discove=
red
galaxy, with three large planets orbiting a star known as Upsilon Andromeda=
e,
is 44 light-years away from Earth.” What is wrong with this statement=
?

28. Figure=
8-4
shows that carbon, nitrogen, and oxygen are among the most abundant elements
(after hydrogen and helium). In our solar system, the atoms of these elemen=
ts
are found primarily in the molecules CH4 (methane), NH3 =
(ammonia),
and H2O (water). Explain why you suppose this is.

=
b>

29. (a) If=
the
Earth had retained hydrogen and helium in the same proportion to the heavier
elements that exist elsewhere in the universe, what would its mass be? Give
your answer as a multiple of the Earth’s actual mass. Explain your
reasoning. (b) How does your answer to (a) compare with the mass of Jupiter,
which is 318 Earth masses? (c) Based on your answer to (b), would you expect
Jupiter’s rocky core to be larger, smaller, or the same size as the
Earth? Explain your reasoning.

*30. If yo=
u start
with 0.80 kg of radioactive potassium (40K), how much will remain
after 1.3 billion years? After 2.6 billion years? After 3.9 billion years? =
How
long would you have to wait until there was no
40K remaining?

*31.
Three-quarters of the radioactive potassium (40K) originally contained=
in a
certain volcanic rock has decayed into argon (40Ar). How long ago did t=
his
rock form?

32. Suppos=
e you
were to use the Hubble Space Telescope to monitor one of the protoplanetary
disks shown in Figure 8-8b. Ove=
r the
course of 10 years, would you expect to see planets forming within the disk?
Why or why not?

33. The
protoplanetary disk at the upper right of Figure 8-8b is seen edge-on. The diameter of the disk is about 700 AU. (a)
Make measurements on this image to determine the thickness of the disk in A=
U.
(b) Explain why the disk will continue to flatten as time goes by.

34. The
accompanying infrared image shows IRAS 04302+2247, a young start that is st=
ill
surrounded by a disk of gas and dust. The scale bar at the lower left of the
image shows that at the distance of IRAS 04302+2247, an angular size of 2
arcseconds corresponds to a linear size of 280 AU. Use this information to =
find
the distance to IRAS 04302+2247.

35. The im=
age
accompanying Question 34 shows a dark, opaque disk of material surrounding =
the
young star IRAS 04302+2247. The disk is edge-on to our line of sight, so it
appears as a dark band running vertically across this image. The material to
the left and right of this band is still falling onto the disk. (a) Make
measurements on this image to determine the diameter of the disk in AU. Use=
the
scale bar at the lower left of this image. (b) If the thickness of the disk=
is
50 AU, find its volume in cubic meters. (c) The total mass of the disk is
perhaps 2 X 10 (to the 28) kg. (0.01 of the mass of the Sun). How many atoms
are in the disk? Assume that the disk is all hydrogen. A single hydrogen at=
om
has a mass of 1.673 X 10 (to the negative 27) kg. (d) Find the number of at=
oms
per cubic meter in the disk. Is the disk material htick or thin compared to=
the
air that you breathe, which contains about 5.4 X 10 (to the 25) atoms per c=
ubic
meter?

36. If the
material in the jet shown in Figure 8-15a
is moving at 200 km/s, how long ago was the material at the far right-hand =
end
of the jet ejected from the star? Give your answer in years. (You will need=
to
make measurements on the image.)

*37. The p=
lanet
discovered orbiting the star 70 Virginis (“70Vir” in Figure 8-1=
7),
59 light years, from Earth, moves in an orbit with semimajor axis 0.48 AU a=
nd
eccentricity 0.40. The period of the orbit is 116.7 days. Find the mass of =
70
Virginis. Compare your answer with the mass of the Sun. (Hint: The planet has far less mass than the star.)

=
u>

*38. Becau=
se of
the presence of Jupiter, the Sun moves in a small orbit of radius 742,000 km
with a period of 11.86 years. (a) Calculate the Sun’s orbital speed in
meters per second. (b) An astronomer on a hypothetical planet orbiting the =
star
Vega, 25 light-years from the Sun, wants to use the astrometric method to
search for planets orbiting the Sun. What would be the angular diameter of =
the
Sun’s orbit as seen by this alien astronomer? Would the Sun’s
motion be discernible if the alien astronomer could measure positions to an
accuracy of 0.001 arcsec? (c) Repeat part (b), but now let the astronomer be
located on a hypothetical planet in the Pleiades star cluster, 360 light-ye=
ars
from the Sun. Would the Sun’s motion be discernible to this astronome=
r?

39. (a) Fi=
gure
8-18c shows how astronomers det=
ermine
that the planet of HD 209458 has a surface temperature of 1130 K. Treating =
the
planet as a blackbody, calculate the wavelength at which it emits most
strongly. (b) The star HD 209458 itself has a surface temperature of 6030 K.
Calculate its wavelength of maximum emission, assuming it to be a blackbody.
(c) If a high-resolution telescope to use visible or infrared light? Explain
your reasoning.

*40. (a) T=
he star
2M1207 shown in Figure 8-20 is 170 light-years from Earth. Find the angular
distance between this star and its planets as seen from Earth. Express your
answer in arcseconds. (b) The mass of 2M1207 is 0.025 that of the Sun; the =
mass
of the planet is very much smaller. Calculate the orbital period of the pla=
net,
assuming that the distance between the start and planet shown in Figure 8-2=
0 is
the semimajor axis of the orbit. Is it possible that an astronomer could
observe a complete orbit in one lifetime?

Chapter 9__________________________________

Review

=
o:p>

=
o:p>

Advanced Q=
uestions

t=
hose
shown in figure 9-21c) Have a green color dominated by emission from
oxygen atoms at a wavelength of 557.7 nm. (a) what minimum energy (in
electron volts) must be imparted to an oxygen atom to make it emit this
wavelength? (b) why is you answer in (a) a minimum value?

Chapter
10________________________________

Review Questions

=

=
1.Is
it correct to say that the Moon orbits the earth? If not, what is a more
correct description?

=
2.If
the moon always keeps the same face toward the earth, how is it possible fo=
r earth
observers to see more than half of the moon’s surface?

=
3.Why
does the sky look black on the moon even during daytime?

=
4.Why
is it impossible for liquid water to exist on the surface of the moon?

=
6.Describe
the kinds of features that can be seen on the moon with small telescopes.=
p>

=
7.Are
impact craters on the moon the same size as the meteoroids that made the
impact? Explain you answer.

=
8.Describe
The differences between the maria and the lunar highlands. Which kind of
terrain covers more of the moon’s surface? Which kind of terrain is m=
ore
heavily cratered? Which kind of terrain was formed later in the moon’s
history? How do we know?

=
9.Describe
the differences between the near and far sides of the moon. What is thought=
to
be the likely explanation for these differences?

=
10.What =
does
it mean to say the moon is a “one-plate world’? What is the
evidence for this statement?

=
11.Why w=
as it
necessary to send unmanned spacecraft to land on the moon before sending hu=
mans
there?

=
12.What =
is the
evidence that ice exists at he lunar poles? Is this evidence definitive?

=
13.Why w=
as it
useful for the Apollo astronauts to bring magnetometers and seismometers to=
the
moon?

=
14.Could=
you
use a magnetic compass to navigate on the moon? Why or why not?

=
15.Descr=
ibe
the evidence that (a) the moon has a more solid interior than the earth and=
(b)
the moon’s interior is not completely solid.

=
16.Expla=
in why
moonquakes occur more frequently when the moon is at perigee than at other
locations along its orbit.

=
17.Why i=
s the
earth geologically active while the moon is not?

=
18.What =
is the
regolith? What causes its powdery character?

=
19.Why a=
re
there no sedimentary rocks on the moon?

=
20.On the
basis of moon rocks brought back by the astronauts, explain why the maria a=
re
dark-colored but the lunar high-lands are light-colored.

=
21.Brief=
ly
describe the main differences and similarities between moon rocks and earth
rocks.

=
22.Rocks=
found
on the moon are between 3.12 and 4.47 billion years old. By contrast, the
majority of the earth’s surface is made of oceanic crust that is less
than 200 million years old, and the very oldest earth rocks are about 4 bil=
lion
years old, if the earth and moon are essentially the same age, why is there
such a disparity in the ages of rocks on the tow worlds?

=
23.If the
earths tidal bulge pointed directly toward the moon, would the moon still be
receding from the earth? Explain.

=
25.Some =
people
who supported the fission theory proposed that the pacific ocean basin is t=
he
scar left when the moon pulled away from the earth. Explain why this idea is
probably wrong.

Advanced Questions

=
26.Su=
ppose
two worlds (say, a planet and its satellite) have masses m1 and m2, and the=
center-to-center
distance between the worlds is r. The distance d cm from the center of worl=
d 1
to the center of mass to the system of two worlds is given by the formula

<=
span
style=3D'mso-spacerun:yes'>

Dc=3Dm2r

&nbs=
p; &=
nbsp;
m1+m2

=
(a)Suppose
world 1 is the earth and world 2 is the moon, If the earthand moon are at their average
center-to-center distance, find the distance from the center of the earth to
the center of mass of the earth-moon system. (b) Is the earth-moon systems
center of mass within the earth? How far below the earth’s surface is=
it
located? (c) find the distance from the center of the sun (mass 1.989x10 to=
the
30 power kg) to the center of mass of the sun-earth system. How does this
compare to the diameter of the sun? Is it a good approximation to say that =
the
earth orbits around the center of the sun?

=
27.If=
you
view the moon through a telescope, you will find that details of its craters
and mountains are more visible when the moon is near first quarter phase or
third quarter phase than when it is at full phase. Explain why.

<=
/u>

=
28.In=
a
whimsical moment during the Apollo 14 mission, astronaut alan Shepard hit t=
wo
golf balls over the lunar surface. Give two reasons why they traveled much
farther than golf balls do on earth.

=
29.Te=
mperature
variations between day and night are much more severe on the moon than on
earth. Explain why.

=
30.Ho=
w much
would an 80-kg person weigh on the moon? How much does that person weigh on=
the
earth?

=
31.Us=
ing
the diameter and mass of the moon given in table 10-1 verify that the
moon’s average density is about 3344 kg/m to the third power. Explain=
why
this average density implies that the moon’s interior contains much l=
ess
iron than the interior of the earth.

=
32.In=
box 10-1 we
calculated the tidal force that the earth exerts on two 1-kg rocks located =
on
the near and far sides of equal to its average value. Repeat this calculati=
on
(a) for the moon at perigee and (b) for the moon at apogee. (c) what is the
ratio of the tidal force on the rocks at perigee to the tidal force at apog=
ee?

=
33.The
youngest lunar anorthosites are 4.0 billion years old, and the youngest mare
basalts are 3.1 billion years old. Would you expect to find any impact brec=
cias
on the moon that formed less than 3.1 billion years ago? Explain you answer=
.

=
34.In=
the
maria, the lunar regolith is about 2 to 8 meters deep. In the lunar highlan=
ds,
by contrast, it may be more than 15 meters deep. Explain how the different =
ages
of the maria and highlands can account for these differences.

=
36.Ca=
lculate
the round-trip travel time for a pulse of laser light that is fired from a
point on the earth nearest the moon, hits a reflector at the point on the m=
oon
nearest the earth, and returns to its point of origin. Assume that the earth
and moon are at their average separation from each other.

=
37.Be=
fore
the Apollo missions to the moon, there were two diametrically opposite scho=
ols
of thought about the history of lunar geology. The “cold moon”
theory held that all lunar surface features were the result of impacts. The
most violent impacts melted the surface rock, which then solidified to form=
the
maria. The opposite “hot moon” theory held that all lunar featu=
res,
including maria, mountains, and craters, were the result of volcanic activi=
ty.
Explain how lunar rock samples show that neither of these theories is entir=
ely
correct.

=
38.Wh=
en the
moon originally coalesced, it may have been only one-tenth as far from the
earth as it is now. (a) when the moon first coalesced, was the earth’=
s tidal
force strong enough to lift rocks off the lunar surface? Explain. (b) compa=
red
with the net tidal force that the earth exerts on the moon today, how many
times larger was the net tidal force on the newly coalesced moon? (this str=
ong
tidal force kept the one axis of the moon oriented toward the earth, and the
moon kept that orientation after it solidified).

Chap=
ter 11

Review Questions

39.Wh=
y is
it impossible to see Mercury or Venus in the sky at midnight?

40.Wh=
y are naked-eye
observations of Mercury best made at dusk or dawn, while telescopic
observations are best made during the day?

41.Why
can’t you see any surface features on Mercury when it is closest to t=
he
Earth?

42.Wh=
y is
it best to view Mars near opposition?Why are some oppositions better than others?

43.Ex=
plain
why Mars can best be viewed from Earth while it is undergoing retrograde
motion.

44.Ex=
plain
why the photograph in Figure 11-4b must have been made during the daytime.<=
o:p>

45.In=
his
1964 science fiction story “The Coldest
Place,” author Larry Niven described the
“dark side” of Mercury as the coldest place in the solar
system.What assumption did h=
e make
about the rotation of Mercury? Did
this assumption turn out to be correct?

46.Wh=
at is
3-to-2 spin-orbit coupling?H=
ow is
the rotation period of an object exhibiting 3-to-2 spin-orbit coupling rela=
ted
to its orbital period?What a=
spects
of Mercury’s orbit cause it to exhibit 3-to-2 spin-orbit coupling? What telescopic observations proved
this?

47.Wh=
y was
it so difficult to determine the rate and direction of Venus’s
rotation?How were these fina=
lly
determined?What is one propo=
sed
explanation for the slow, retrograde rotation of Venus?

48.Ex=
plain
why Mercury does not have a substantial atmosphere.

49.Wh=
at
kind of surface features are found on Mercury?How do they compare to surface fea=
tures
on the moon?Why are they pro=
bably
much older than most surface features on the Earth?

50.Ho=
w do
we know that the scarps on Mercury are younger than the lava flows?How can you tell that the scarp in
Figure 11-10 is younger than the vertically distorted crater at the center =
of
the figure?

51.If
Mercury is the closest planet to the Sun and has such a high average surface
temperature, how is it possible that ice might exist on its surface?

=
o:p>

52.Wh=
y do
astronomers think that Mercury has a very large iron core?

=
p>

53.Wh=
y is
it surprising that Mercury has a global magnetic field?Why does the 58.646-day rotation p=
eriod
of Mercury imply that the planet can have only a weak magnetic field?

<=
/o:p>

54.Ho=
w is
Mercury’s magnetosphere similar to that of the Earth?How is it different?Why do you suppose Mercury does no=
t have
Van Allen belts?

55.Wh=
y was
it difficult to determine Venus’s surface temperature from Earth?How was this finally determined?

56.The
Mariner 2 spacecraft did not enter Venus’s atmosphere, but it was
nonetheless able to determine that the atmosphere is very dry.How was this done?

<=
/p>

57.Wh=
y did
Earth observers report that they had seen straight-line features
(“canals”) on Mars? How
did the seasonal winds trick them into thinking Mars had vegetation?

=
o:p>

58.Do=
Venus
and Mars have continents like those on Earth?

59.Wh=
at is
the Martian crustal dichotomy? What
is the evidence that the southern highlands are older than the northern
lowlands?

60.Wh=
at is
the evidence that the surface of Venus is only about 500 million years old?=

61.Wh=
at is
flake tectonics?Why does Ven=
us
exhibit flake tectonics rather than plate tectonics?

62.Wh=
at
geologic features (or lack thereof) on Mars have convinced scientists that
plate tectonics did not significantly shape the Martian surface?

=

63.Wh=
at
geologic processes are thought to have created Valles Marineris?

64.Co=
mpare
the volcanoes of Venus, the Earth, and Mars.Cite evidence that hot-spot volcan=
ism is
or was active on all three worlds.

65.De=
scribe
the evidence that there has been recent volcanic activity (a) on Venus and =
(b)
on Mars.

66.Su=
ppose
all of Venus’s volcanic activity suddenly stopped. (a) How would this
affect Venus’s clouds? (b) How would this affect the overall Venusian
environment?

67.Wh=
y are
the patterns of convection in the Venusian atmosphere so different from tho=
se
in our atmosphere?

68.Wh=
y is
it impossible for liquid water to exist on Mars today?If liquid water existed on mars in=
the
past, what must have been different then?

69.Wh=
y does
the atmospheric pressure on mars vary with the seasons?What is the relationship between t=
his
pressure variation and Martian dust storms?

70.Wh=
y is
it reasonable to assume that the primordial atmospheres of the Earth, Venus,
and Mars were roughly the same?

71.Ca=
rbon
dioxide accounts for about 95% of the present-day atmospheres of both mars =
and
Venus.Why, then, is there a =
strong
greenhouse effect on Venus but only a weak greenhouse effect on Mars?

<=
/o:p>

72.(a=
) What
is a runaway greenhouse effect? (b) What is a runaway icehouse effect?

=

73.Wh=
at is
a dust devil?Why would you f=
eel
much less breeze from a Marian dust devil than from a dust devil on Earth?<=
o:p>

74.(a=
) Why
is Mars red? (b) Why is the Marian sky the color of butterscotch?

75.We=
re the
Viking Landers able to determine whether life currently exists on mars or
whether it once existed there? Why
or why not?

76.(a=
) The
Spirit rover found the minerals olivine and pyroxene at its landing site on
Mars.Explain how this shows =
that
there has been no liquid water at that site for billions of years. (b) What
evidence did the Opportunity rover find =
at its
landing site to suggest that liquid water had once been present there?

=

77.Ho=
w was
the Mars Odyssey spacecraft able to detect water beneath the Martian surface
without landing on the planet?

78.A =
full
moon on Earth is bright enough to cast shadows.As seen from the Martian surface, =
would
you expect a full Phobos or full Deimos to cast shadows?Why or why not?

Chap=
ter 12

Review Questions

1.Mars
passes closer to the Earth than Jupiter does, but with an Earth-based teles=
cope
it is easier to see details on Jupiter than on Mars.Why is this?

2.Saturn
is the most distant of the planets visible without a telescope.Is there any way we could infer th=
is
from naked-eye observations?Explain.

3.As
seen from Earth, does Jupiter or Saturn undergo retrograde motion more
frequently?Explain your answ=
er.

4.In
what ways are the motions of Jupiter’s atmosphere like the motion of
water stirred in a pot (see figure 12-3b)?=
In what ways are they different?

5.Is
the chemical composition of Jupiter as a whole the same as that of its
atmosphere?Explain any diffe=
rence.

6.Astronomers
can detect the presence of hydrogen in stars by looking for the characteris=
tic
absorption lines of hydrogen in the star’s visible spectrum (Figure
5-21).They can also detect
hydrogen in glowing gas clouds by looking for hydrogen’s characterist=
ic
emission lines (Figure 5-18).Explain why neither of these techniques helped Earth-based astronome=
rs
to detect hydrogen in Jupiter’s atmosphere.

7.On
a warm, humid day, water vapor remains in the atmosphere.But if the temperature drops sudde=
nly,
the water vapor forms droplets, clouds appear, and it begins to rain.Relate this observation to why the=
re is
relatively little helium in Saturn’s atmosphere compared to the
atmosphere of Jupiter.

8.What
would happen if you tried to land a spacecraft on the surface of Jupiter?

9.What
are the belts and zones in the atmosphere of Jupiter and Saturn?Is the Great Red Spot more like a =
belt
or a zone?Explain your answe=
r.

11.Wh=
at are
white ovals and brown ovals?=
What
can we infer about them from infrared observations?

12.Co=
mpare
and contrast the source of energy for motions in the Earth’s atmosphe=
re
with the energy source for motions in the atmospheres of Jupiter and Saturn=
.

13.Bo=
th
Jupiter and Saturn emit mire energy than they receive from the Sun in the f=
orm
of sunlight.Compare the inte=
rnal
energy sources of the two planets that produce this emission.

14.Wh=
at
observations from the Cassini spacecraft contradict the accepted picture of
convection in Jupiter’s atmosphere?

15.Co=
mpare
the atmospheres of Jupiter and Saturn.&nbs=
p;
Why does Saturn’s atmosphere look “washed out” in
comparison with that of Jupiter?

16.Wh=
ich
data from the Galileo Probe were in agreement with astronomer’s
predictions?Which data were
surprising?

17.Fe=
wer
than one in every 105 atoms in Jupiter’s atmosphere is an
argon atom, and fewer than one in 108 is an atom of krypton and
xenon.If these atoms are so =
rare,
why are scientists concerned about them?&n=
bsp;
How do the abundances of these elements in Jupiter’s atmosphere
compare to the abundances in the Sun?What hypotheses have been offered to explain these observations?

18.Wh=
y is
Jupiter oblate?What do astro=
nomers
learn from the value of Jupiter’s oblateness?

19.Wh=
at is
liquid metallic hydrogen?Wha=
t is
its significance for Jupiter?

20.De=
scribe
the internal structures of Jupiter and Saturn, and compare them with the
internal structure of the Earth.

21.Ex=
plain
why Saturn is more oblate than Jupiter, even though Saturn rotates more slo=
wly.

22.If
Jupiter does not have any observable solid surface and its atmosphere rotat=
es
differentially, how are astronomers able to determine the planet’s
internal rotation rate?

23.co=
mpare
and contrast Jupiter’s magnetosphere with the magnetosphere of a
terrestrial planet like Earth. Why
is the size of the Jovian magnetosphere highly variable, while that of the
Earth’s magnetosphere is not?

24.Wh=
at is
a plasma?Where are plasmas f=
ound
in the vicinity of Jupiter?

25.Wh=
y is
Saturn’s magnetosphere less extensive than Jupiter’s?

26.Wh=
at
observations of Saturn’s rings proved that they are not solid?

=
o:p>

27.If
Saturn’s rings are not solid, why do they look solid when viewed thro=
ugh
a telescope?

28.Al=
though
the Voyager and Cassini spacecraft did not collect any samples of
Saturn’s ring particles, measurements from these spacecraft allowed
scientists to determine the sizes of the particles.Explain how this was done.

29.The
Space Shuttle and other spacecraft orbit the Earth well within the
Earth’s Roche limit.Ex=
plain
why these spacecraft are not torn apart by tidal forces.

30.Ho=
w do
Jupiter’s rings differ from those of Saturn?

31.De=
scribe
the structure of Saturn’s rings.&nbs=
p;
What evidence is there that ring particles do not migrate significan=
tly
between ringlets?

32.Du=
ring
the planning stages for the Pioneer 11 mission, when relatively little was
known about Saturn’s rings, it was proposed to have the spacecraft fly
through the Cassini division.Why
would this have been a bad idea?

33.Wh=
at is
the relationship between Saturn’s satellite Mimas and the Cassini
division?

34.Wh=
y is
the term “shepherd satellite” appropriate for the objects so
named?Explain how a shepherd
satellite operates.

Chapter
13__________________________________

1. =
If you observed the Galilean satellites through a telesc=
ope
for a single night, could you notice their motions around Jupiter?

2. =
Why can’t the Galilean satellites be seen with the
naked eye?

3. =
During the time it takes Ganymede to complete one orbit,=
how
many orbits do Io and Europa complete?

4. =
In what ways does the system of Galilean satellites rese=
mble
our solar system? In what ways is it different?

5. =
No spacecraft from Earth has ever landed on any of the
Galilean satellites. How, then, can we know anything about the chemical
compositions of these satellites?

6. =
In what ways did the formation of the Galilean satellites
mimic the formation processes different?

7. =
In the classic science-fiction film 2010: The Year We Ma=
ke
Contact, an alien intelligence causes Jupiter to contract so much that nucl=
ear
reactions begin at its center. As a result, Jupiter becomes a star like the
Sun. Is this possible in principle? Explain your answer.

<=
/p>

8. =
All of the Galilean satellites orbit Jupiter in the same
direction.Furthermore, the p=
lanes
of their orbits all lie within 0.5of Jupiter’s equatorial plane. Explain why these observations =
are
consistent with the idea that the Galilean satellite formed from a
“Jovian Nebula.”

9. =
What is the source of energy that powers Io’s
volcanoes? How is it related to the orbits of Io and the other Galilean
satellites?

10.Io has no
impact craters on its surface, while our Moon is covered with crates.What is the explanations for this
difference?

11.Despite =
all
the gases released from its interior by volcanic activity, Io does not poss=
ess
a thick atmosphere.Explain w=
hy
not.

12.Long bef=
ore
the Voyager flybys, Earth-based astronomers reported that Io appeared brigh=
ter
than usual for the few hours after it emerged from Jupiter’s shadow.<=
span
style=3D'mso-spacerun:yes'> From what we know about the materi=
al
ejected from Io’s volcanoes, suggest an explanation for this brief
brightening of Io.

13.How do l=
avas
on Io differ from typical lavas found on Earth?What does this difference tell us =
about
Io’s interior?

14.What acc=
ounts
for the different colors found on Io’s surface?

15.What is =
the Io
torus? What is its source?

16.What is =
the
origin of the electric current that slows through Io.

17.How was =
the
Galileo spacecraft used to determine the internal structure of Io and the o=
ther
Galilean satellites?

26.Why are
numerous impact craters found on Ganmede and Callisto but not on Io or Euro=
pa?

27.Describe=
the
surprising aspects of Callisto’s surface and interior that were revea=
led
by the Galileo spacecraft. Why did these come as a surprise?

28.Compare =
and
contrast the surface features of the four Galilean satellites. Discuss their
relative geological activity and the evolution of these four satellites.

29.The larg=
er the
orbit of a Galilean satellite, the less geologic acivivty that satellite ha=
s.
Explain why.

30.Explain =
how
the 1:2:4 ratio of the orbital periods of Io, Europa, and Ganymede is relat=
ed
to the geologic activity on these satellites.

31.Describe
Titan’s atmosphere. What effect has the Sun’s ultraviolet radia=
tion
had on Titan’s atmosphere?

32.In what =
ways
do hydrocarbons on Titan behave like water on Earth?

33.Why does=
the
presence of methane in Titan’s atmosphere imply that Titan has had re=
cent
volcanic activity?

34.What is =
the
evidence that there were liquid hydrocarbons on Titan in the past? That the=
re
are liquid hydrocarbons now?

35.How woul=
d you
account for the existence of the satellites of Jupiter other than the Galil=
ean
ones?

36.Which of
Saturn’s moderate-sized satellites show evidence of geologic activity?
What might be the energy source for the acitivity?

37.Explain =
why
debris from Phoebe would be expected to pile up only on the leading hemisph=
ere
of Iapetus. (Hint: How do the orbits of these two satellites compare? How d=
oes
the orbital motion of debris falling slowly inward toward Saturn compare wi=
th
the orbital motion of Iapetus?)

38.Saturn=
8217;s
equator is tilted by 27 degree from the ecliptic, while Jupiter’s equ=
ator
is tilted by only 3 degrees. Use these data to explain why we see fewer
transits, eclipses, and occultations of Saturn’s satellites than of t=
he
Galilean satellites.

Chapter 14__________________________________

<=
/span>

Cou=
ld
astronomers in antiquity have seen Uranus? If so, why was it not
recognized as a planet?

Why=
do
you suppose that the discovery of Neptune
is rated as one of the great triumphs of science, whereas the discover=
ies
of Uranus and Pluto are not?

Why=
is it
so difficult to see features in the atmosphere of Uranus?

=
span>

(a)=
Draw
a figure like Figure 14-3, and indicate on it where Uranus was in 1986=
and
2004. Explain you reasoning. (Hint: See Figure 14-1 and Figure 14-2.) =
(b)
In approximately what year will the Sun next be highest in the sky as =
seen
from Uranus’s south pole? Explain your reasoning.

Why=
do
you suppose the tilt of Uranus’s rotation axis was deduced from =
the
orbits of its satellites and not by observing the rotation of the plan=
et
itself?

Des=
cribe
the seasons on Uranus. In what ways are the Uranian seasons different =
from
those on Earth?

Exp=
lain
the statement “Methane is to Uranus’s atmosphere as water =
is
to Earth’s atmosphere.”

A n=
umber
of storms in the Uranian atmosphere can be seen in Figure 14-2, but no=
ne
are visible in Figure 14-1. How can you account for the difference.

Why=
are
Uranus and Neptune distinctly blue-green in color, while Jupiter or Sa=
turn
are not?

How=
does
the energy source for Uranus’s atmospheric motions differ from t=
hose
from Jupiter, Saturn, and Neptune?

Why=
are
fewer white clouds seen on Uranus and Neptune than on Jupiter and Satu=
rn?

Why=
do
Uranus and Neptune have higher densities than Jupiter and Saturn?

=

Dis=
cuss
some competing explanations of why Uranus and Neptune are substantially
smaller than Jupiter and Saturn.

How=
do
the orientations of Uranus and Neptune’s magnetic axes differ fr=
om
those of other planets?

Bri=
efly
describe the evidence supporting the idea that Uranus was struck by a
large planet like object several billion years ago.

The=
1977
occultation that led to the discovery of Uranus’s rings was visi=
ble
from the Indian Ocean. Explain why =
it
could not be seen from other parts of the Earth’s night side.

As
voyager 2 flew past Uranus, it produced images only of the southern
hemispheres of the planet’s satellites. Why do you suppose this =
was?

Why=
do
astronomers think that the energy needed to resurface parts of Miranda
came from tidal heating rather than the satellite’s own internal
heat?

Usi=
ng the
data in Appendix 3, explain why Uranus’s satellites Caliban and
Sycorax (both discovered in 1997) were probably captured from space ra=
ther
than having formed and the same time as the planet itself.

<=
/span>

Bri=
efly
describe the evidence supporting the idea that Triton was captured by =
Neptune.

If =
you
were floating in a balloon in Neptune’s
upper atmosphere, in what part of the sky would you see Triton rise? E=
xplain
your reasoning.

Why=
is it
reasonable to suppose that Neptune =
will
someday be surrounded by a broad system of rings, perhaps similar to t=
hose
that surround Saturn?

How=
can
astronomers distinguish a faint solar system object like Pluto from
background stars within the same field of view?

Wha=
t is
the vidence that the three moon of Pluto have common origin?

How=
do
the presence of Pluto’s moon suggest the there must be other wor=
lds
beyond Neptune?

=
li>

Why=
are
there a large number of objects with the same semi-major axis as Pluto=
?

Are=
there
any trans-Neptunian objects that are not members of the Kuiper belt? A=
re
there any members of the Kuiper that are not trans-Neptunian objects?
Explain.

See =
Box
1-1 for the small-angle formula. Recall that the volume of=
a
sphere of radius r is 4πr3/3. Section 4-7 discusses the
gravitational force between two objects and Newton’s form of Kepler’s=
third
law. You will find discussions of the original form of Kepler’s thi=
rd
law in Section 4-4, tidal forces in Section 4-8, Wien’s law for
blackbody radiation in Section 5-4, and the transparency of the EarthR=
17;s
atmosphere to various wavelengths of light in Section 6-7.

29. F=
or which
configuration of the Sun, Uranus, and Neptune is the gravitational force of=
Neptune on Uranus at a maximum? For this configurat=
ion,
calculate the gravitational force exerted by the Sun on Uranus and by Neptune on Uranus. Then calculate the fraction by w=
hich
the sunward gravitational pull on Uranus is reduced by Neptune
at that configuration. Based on your calculations, do you expect that Neptune has a relatively large or relatively small =
effect
on Uranus’s orbit?

30. At
certain points in its orbit, a stellar occultation by Uranus would not reve=
al
the existence of the rings. What points are those? How often does this
circumstance arise? Explain using a diagram.

31. A=
ccording
to one model for the internal structure of Uranus, the rocky core and the
surrounding shell of water and methane ices together make up 80% of the
planet’s mass. This interior region extends from the center of Uranus=
to
about 70% of the planet’s radius. (a) Find the average density of this
interior region. (b) How does your answer to (a) compare with the average
density of Uranus as a whole? Is this what you would expect? Why?

32. U=
ranus’s
epsilon (e)
ring has a radius of 51, 150 km. (a) How long odes it take a particle in th=
e ering to make one compl=
ete
orbit of Uranus? (b) If you were riding on one of the particles in the =
e ring and watching a c=
loud
near Uranus’s equator, would the cloud appear to move eastward or
westward as Uranus rotates? Explain your answer.

33. S=
uppose
you were standing on Pluto. Describe the motions of Charon relative to the =
Sun,
the stars, and your own horizon. Would you ever be able to see a total ecli=
pse
of the Sun? (Hint: You will need to calculate the angles subtended by Charon
and by the Sun as seen by an observer on Pluto.) In what circumstances would
you never see Charon?

34. I=
t is
thought that Pluto’s tenuous atmosphere may become even thinner as the
planet moves toward aphelion (which it will reach in 2113), then regain its
present density as it again moves toward perihelion. Why should this be?

35. T=
he
brightness of sunlight is inversely proportional to the square of the dista=
nce
from the Sun. For example, at a distance of 4 AU from the Sun, sunlight is =
only
(1/4)2 =3D 1/16 =3D 0.0625 as bright as at 1 AU. Compared with t=
he
brightness of sunlight on the Earth, what is its brightness (a) on Pluto at
perihelion (29.649 AU from the Sun) and (b) on Pluto at aphelion (49.425 AU
from the Sun)? (c) How much brighter is it on Pluto at perihelion compared =
with
aphelion? (Even this brightness is quite low. Noon on Pluto is about as dim=
as
it is on the Earth a half hour after sunset on a moonless night.)

*36. If
Earth-based telescopes can resolve angles down to 0.25 arcsec, how large co=
uld
a trans-Neptunian object be at Pluto’s average distance from the Sun =
and
still not present a resolvable disk?

37. T=
he
observations of Pluto shown in Figure 14-19 were made using blue and
ultraviolet light. What advantages does this have over observations made wi=
th
red or infrared light?

*38. Calculate
the maximum angular separation between Pluto and Charon as seen from Earth.
Assume that Pluto is at perihelion (29.649 AU from the Sun) and that Pluto =
is
at opposition as seen from Earth.

39. P=
resumably
Pluto and Charon raise tidal bulges on each other. Explain why the average
distance between Pluto and Charon is probably constant, rather than increas=
ing
like the Earth-Moon distance or decreasing like the Neptune-Triton distance.
Include a diagram like Figure 10-17 as part of your answer.

40. (=
a) Find
the semimajor axis of the orbit of an object whose period is 3/2 of the orb=
ital
period of Neptune. How does your result
compare to the semimajor axis of Pluto’s orbit? (b) A number of Kuiper
belt objects called plutinos have been discovered with the same orbital per=
iod
and hence the same semimajor axis as Pluto. Explain how these objects can a=
void
colliding with Pluto.

41. F=
ind the
semimajor axis of the orbit of an object whose period is twice the orbital
period of Neptune. How does your result
compare to the outer limit of the Kuiper belt?

42. S=
uppose
you wanted to search for trans-Neptunian objects. Why might it be advantage=
ous
to do your observations at infrared rather than visible wavelengths? (Hint:=
At
visible wavelengths, the light we see from planets is reflected sunlight. At
what wavelengths would you expect distant planets to emit their own light m=
ost
strongly? Use Wien’s law to calculate the wavelength range best suited
for your search.) Could such observations be done at an observatory on the
Earth’s surface? Explain.

43. T=
he New
Horizons spacecraft will swing by Jupiter to get a boost from that
planet’s gravity, enabling it to reach Pluto relatively quickly. To s=
ee what
would happen if this technique were not used, consider a spacecraft traject=
ory
that is an elliptical orbit around the Sun. The perihelion of this orbit is=
at
1 AU from the Sun (at the Earth) and the aphelion is at 30 AU (at PlutoR=
17;s
position). Calculate how long it would take a spacecraft in this orbit to m=
ake
the one-way trip from Earth to Pluto. Based on the information in Section
14-10, how much time is saved by making a swing by Jupiter instead?

Chapter 15__________________________________

1. What led astronomers to suspect that here were m=
embers
of the solar system that orbit between Mars & Jupiter?

=
p>

2. How did the first asteroid come to be discovered=
?

&nbs=
p; What
role did theoretical calculations play in confirming the discovery?

&nbs=
p; How
did this discovery differ from what astronomers had expected to find?

<=
/o:p>

3. How do modern astronomers discover new asteroids=
?

4. What are the differences between asteroids &
trans-Neptunian objects?

5. Describe the asteroid belt.

&nbs=
p; Does
it lie completely within the plane of the ecliptic?

&nbs=
p; What
are its inner and outer radii?

6. If Jupiter was not present in our solar system, =
would
the asteroid belt exist?

&nbs=
p; Why
or why not?

7. What are Kirkwood
gaps?

&nbs=
p; What
causes them?

8. Compare the explanation of the Kirkwood gaps in =
the
asteroid belt o the way in which Saturn’s moons help produce division=
in
that planet’s rings.

9. How is it possible to tell that some asteroids a=
re
non-spherical even though we do not have images of those asteroids?

10. What is the evidence that some asteroids are ma=
de of
a loose conglomeration of smaller pieces?

11. The asteroid 243 Ida, which was viewed by the G=
alileo
spacecraft, is a member of a Hirayama family.Discuss what this tells us about t=
he
history of this asteroid.

&nbs=
p; Where
might you look to find other members of the same family.

12. What are the Trojan asteroids, and where are th=
ey
located?

&nbs=
p; What
holds them in this location?

13. What are near-Earth objects?

&nbs=
p; What
is the evidence that the Earth has been struck by these objects?

=

14. What is the evidence that an asteroid impact co=
uld
have contributed to the demise of the dinosaurs?

15. What is the difference between a meteoroid, a m=
eteor,
and a meteorite?

16. Is there anywhere on the Earth where you might =
find
large numbers of stony meteorites that are not significantly weathered?

&nbs=
p; If
so, where?If not, why not?

17. Scientists can tell that certain meteorites cam=
e from
the interior of an asteroid rather than from its outer layers.Explain how this is done.

18. Why are some asteroids differentiated while oth=
ers
are not?

19. Suppose you found a rock you suspect might be a
meteorite.Describe some of t=
he
things you could do to determine whether it was a meteorite or a “met=
eor
wrong”

20. What is the evidence that carbonaceous chondrit=
es are
essentially unaltered relics of the early solar system?

&nbs=
p; What
do they suggest about how the solar system may have formed?

<=
/p>

21. With the aid of a drawing, describe the structu=
re of
a comet.

22. Why is the phrase “dirty snowball” =
an
appropriate characterization of a comets nucleus?

23. What did scientist learn about the structure of=
comet
nuclei from the Deep Impact mission?

24. Why do the ion tail & dust tail of a comet =
point
in different directions?

25. Why do comets have prominent tails for only a s=
hort
time during each orbit?

26. Why is it that Jupiter & Saturn can be seen=
in
the night sky every year, while seeing specific comets such as Halley &
Hyakutake is a once in a lifetime event?

27. What are the relationship between the Kuiper be=
lt and
comets?

28. What is the Oort cloud?

&nbs=
p; How
might it be related to planetesimals left over from the formation of the so=
lar &=
nbsp; system?

29. Why are comets more likely to break apart at
perihelion than at aphelion?

The small-angle formula is described in Box 1-1. We
discussed retrograde motion in Section 4-1 and described its causes in
Section 4-2. You will need to use Kepler’s third law, described in
Section 4-4 and Box
4-2, in some of the problems below. Box 7-2 discusses the concept of =
escape
speed. A spherical object of radius r intercepts an amount of sunlight
proportional to its cross-sectional area, equal to πr2. T=
he
volume of a sphere of radius r is 4πr3/3.

32. When Olbers discovered Pallas in March 1802, the
asteroid was moving from east to west relative to the stars. At what time of
night was Pallas highest in the sky over Olbers’s observatory? Explain
your reasoning.

33. Consider the Kirkwood
gap whose orbital period is two-fifths of Jupiter’s 11.86-year period.
Calculate the distance from the Sun to this gap. Does your answer agree with
Figure 15-4?

*34. When the image in Figure 15-5 was made, the as=
teroid
1 Ceres was 1.63 AU, or 2.44 x 108 km, from the Hubble Space
Telescope. (a) What was the angular size of the asteroid as a whole? (b) You
can see individual pixels in the mage shown in Figure 15-5. Using a ruler a=
nd
the scale bar in the figure, determine how many kilometers on the surface o=
f 1
Ceres are contained in the width of one pixel. (c) What is the angular widt=
h of
each pixel in arcseconds?

35. Suppose that a binary asteroid (two asteroids
orbiting each other) is observed in which one member is 16 times brighter t=
han
the other. Suppose that both members have the same albedo an that the large=
r of
the two is 120 km in diameter. What is the diameter of the other member?

36. The accompanying image from the Galileo spacecr=
aft
shows the asteroid 243 Ida, which has dimensions 56 x 24 x 21km. Galileo
discovered a tiny moon called Dactyl, just 1.6 x 1.4 x 1.2km in size, which
orbits Ida at a distance of about 100 km. (In Greek mythology, the Dactyli =
were
beings who lived on the slopes of Mount Ida.) Describe a scenario that could
explain how Ida came to have a moon.

*37. Assume that Ida’s tiny moon Dactyl (see
Question 36) has a density of 2500 kg/m3. (a) Calculate the mass=
of
Dactyl in kilograms. For simplicity, assume that Dactyl is a sphere 1.4 km =
in
diameter. (b) Calculate the escape speed from the surface of Dactyl. If you
were an astronaut standing on Dactyl’s surface, could you throw a
baseball straight up so that it would never come down? Professional baseball
pitchers can throw at speeds around 40 m/s (140 km/h, or 90 mi/h); your
throwing speed is probably a bit less.

38. Imagine that you are an astronaut standing on t=
he
surface of a Trojan asteroid. How will you see the phase of Jupiter change =
with
the passage of time? How will you see Jupiter move relative to the distant
stars? Explain your answers.

39. Use the percentages of stones, irons, and stony=
iron
meteorites that fall to Earth to estimate what fraction of their parent
asteroids’ interior volume consisted of an iron core. Assume that the
percentages of stones and irons that fall to the Earth indicate the fractio=
ns
of a parent asteroid’s interior volume occupied by rock and iron,
respectively. How valid do you think this assumption is?

40. On March 8, 1997, Comet Hale-Bopp was 1.39 AU f=
rom
the Earth and 1.00 AU from the Sun. Use this information and that given in =
the
caption to Figure 15-24 to estimate the length of the comet’s ion tai=
l on
that date. Give your answer in kilometers and astronomical units.

41. Sun-grazing comets come so close to the Sun that
their perihelion distances are essentially zero. Find the orbital periods of
Sun-grazing comets whose aphelion distances are (a) 100 AU, (b) 1,000 AU, (=
c)
10,000 AU, and (d) 100,000 AU. Assuming that these comets can survive only a
hundred perihelion passages, calculate their lifetimes. (Hint: Remember that
the semimajor axis of an orbit is one-half the length of the orbit’s =
long
axis.)

42. Comets are generally brighter a few weeks after
passing perihelion than a few weeks before passing perihelion. Explain why
might this be. (Hint: Water, including water ice, does an excellent job of
retaining heat.)

43. The hydrogen envelopes of comets are especially
bright at an ultraviolet wavelength of 122 nm. Use Figure 5-24 to explain w=
hy.

44. A very crude model of a typical comet nucleus i=
s a
cube of ice (density 1,000 kg/m3) 10 km on a side. (a) What is t=
he mass
of this nucleus? (b) Suppose 1% of the mass of the nucleus evaporates away =
to
form the comet’s tail. Suppose further that the tail is 100 million (=
108)
km long and 1 million (106) km wide. Estimate the average densit=
y of
the tail (in kg/m3). For comparison, the density of the air you
breathe is about 1.2 kg/m3. (c) In 1910 the Earth actually passed
through the tail of Comet Halley. At the time there was some concern among =
the
general public that this could have deleterious effects on human health. Wa=
s this
concern justified? Why or why not?

45. For many years it was thought that the Tunguska event was caused by a comet striking the E=
arth.
This idea was rejected because a small comet would have broken up too high =
in
the atmosphere to cause significant damage on the ground. Explain why, using
your knowledge of a comet’s structure.

Chapter 16 __________________________________

=

=

1. What is meant by the luminosity of the Sun?

=

2. What is Kelvin-Helmholtz contraction?

=

&nbs=
p; Why
is it ruled out as a source of the present-day Sun’s energy?

3. Why is it impossible for the burning of substanc=
es
like coal to be the source of the Sun’s energy?

4. What is hydrogen fusion?

&nbs=
p; Why
is hydrogen fusion fundamentally unlike the burning of a log in a fireplace=
?

5. If the electric force between protons were someh=
ow
made stronger, what effect would this have on the temperature required for
thermonuclear fusion to take place?

6. Why do thermonuclear reactions occur only in the
Sun’s core, not in its outer regions?

&nbs=
p; Describe
how the net result of the reactions shown in Cosmic Connections figure =
&=
nbsp; (Section
16-1) is the conversion of four protosun into a single helium nucleus.

&nbs=
p; What
other particles are produced in this process?

&nbs=
p; How
many of each particles are produced?

8. Give an everyday example of hydrostatic equilibr=
ium.

Give an example of thermal equilibrium.

<=
/u>

&nbs=
p; Explain
how these equilibrium conditions apply to each example.

9. If thermonuclear fusion in the Sun were suddenly=
to stop,
what would eventually happen to the overall radius of the Sun?

&nbs=
p; What
solution to this problem was suggested by the results from the SudburyNeutrino
Observatory?

17. Describe the dangers in attempting to observe t=
he
Sun.How have astronomers lea=
rned
to circumvent these observational problems?

18. Briefly describe the three layers that make up =
the
Sun’s atmosphere.

=

&nbs=
p; In
what ways do they differ from each other?

19. What is solar granulation?

&nbs=
p; Describe
how convection gives rise to granules.

20. High-resolution spectroscopy of the photosphere
reveals that absorption lines are blue shifted in the spectrum of the centr=
al,
bright regions of granules but are redshifted in the spectrum of the dark
boundaries between granules but are redshifted in the spectrum of the dark
boundaries between granules.Explain how these observations show that granulation is due to
convection.

&nbs=
p;

21. What is the difference between granules and sup=
er
granules?

22. What are spicules?

&nbs=
p;

&nbs=
p; Where
are they found?

&nbs=
p; How
can you observe them?

&nbs=
p; What
causes them?

23. How do astronomers know that the temperature of=
the
corona is so high?

24. How do astronomers know when the next sunspot m=
aximum
and minimum will occur?

25. Why do astronomers say that the solar cycle is =
really
22 years long, even though the number of sunspots varies over an 11-year pe=
riod?

26. Explain how the magnetic-dynamo model accounts =
for
the solar cycle.

27. Describe one explanation for why the corona has=
a
higher temperature than the chromosphere.

Exp=
lain
the difference between a star’s apparent brightness and its
luminosity.

Des=
cribe
how the parallax method of finding a start’s distance is similar=
to
binocular (two-eye) vision in humans.

Why=
does
it take at least six months to make a measurement of a star’s
parallax?

Why=
are
measurements of stellar parallax difficult to make?

<=
/li>

What are the advantages of making t=
hese
measurements from orbit?

Wha=
t is
the inverse-square law? Use it to explain why an ordinary light bulb c=
an
appear brighter than a star, even though the light bulb emits far less
light energy per second.

Bri=
efly
describe how you would determine the luminosity of a nearby start.Of what value is knowing the
luminosity of various stars?

Whi=
ch are
more common, stars more luminous than the sun or stars less luminous than the sun?

Why=
is
the magnitude scale called a “backward” scale? What is the
difference between apparent magnitude and absolute magnitude?

The=
star
Zubenelgenubi (from the Arabic for “scorpion’s southern
claw”) has apparent magnitude +2.75, while the star Sulafat (Ara=
bic
for “tortoise”) has apparent magnitude +3.25.Which star appears brighter? =
From this information alone, w=
hat
can you conclude about the luminosities of these starts? Explain.

=

Exp=
lain
why the color ratios of a star are related to the star’s surface
temperature.

Wou=
ld it
be possible for a star to appear bright when viewed through a U filter=
or
a V filter, but dim when viewed through a B filter? Explain.

Men=
kalinan
(Arabic for “shoulder of the rein-holder”) is an A2 star in
the constellation Auriga (the Charioteer).What is its spectral class? What is its spectal type? Whi=
ch
gives a more precise description of the spectrum of Menkalinan?

=
o:p>

Wha=
t are
the most prominent absorption lines you would expect to find in the sp=
ectrum
of a star with a surface temperature of (a) 35,000 K, (b) 2800 K, and =
(c)
580 K (like the Sun”?Briefly describe why these stars have such different spectra ev=
en
though they have essentially the same chemical composition.

=

A f=
ellow
student expresses the opinion that since the Sun’s spectrum has =
only
weak absorption lines of hydrogen, this element cannot be a major
constituent of the Sun.=
How
would you enlighten this person?

If =
a red
star and a blue star both have the same radius and both are the same
distance from the Earth, which one looks brighter in the night sky?
Explain why.

If =
a red
star and a blue star both appear equally bright and both are the same
distance from the Earth, which one has the larger radius?Explain why.

If =
a red
star and a blue star both have the same radius and both appear equally
bright, which one is farther from Earth?Explain why.

Mos=
t of
the bright stars in the night sky (see Appendix 5) are giants and
supergiants.How can thi=
s be,
if giants and supergiants make up only 1 % of the population of stars?=

Exp=
lain
why the dashed lines in Figure 17-15b slope down and to the right.

Some
giant and supergiant stars are of the same spectral type (G2) as the
Sun.What aspects of the
spectrum of a G2 star would you concentrate on to determine the
star’s luminosity class?Explain what you would look for.

Bri=
efly
describe how you would determine the distance to a star whose parallax=
is
too small to measure.

What
information stars do astronomers learn from binary systems that cannot=
be
learned in any other way? What
measurements do they make of binary systems to garner this information=
?

Sup=
pose
that you want to determine the temperature, diameter, and luminosity o=
f an
isolated star (not a member of a binary system). Which of these physic=
al
quantities require you to know the distance to the star?Explain.

Wha=
t is
the mass-luminosity relation? Does it apply to stars of all kinds?

Use
Figure 17-21 to (a) estimate the mass of a main-sequence star that is =
1000
times as luminous as the Sun, and (b) estimate the luminosity of a
main-sequence star whose mass is one-fifth that of the Sun.Explain your answers.

Whi=
ch is
more massive, a red main-sequence star of a blue main-sequence star? Which has the greater radius?
Explain your answers.

How=
do
while dwarfs differ from brown dwarfs? Which are more massive? Which a=
re
larger in radius? Which are denser?

Ske=
tch
the redial velocity curves of a binary consisting of two identical sta=
rs
moving in circular orbits that are (a) perpendicular to and (b) parall=
el
to our line of sight.

Giv=
e two
reasons why a visual binary star is unlikely to also be a spectroscopic
binary star.

Ske=
tch
the light curve of an eclipsing binary consisting of two identical sta=
rs
in highly elongated orbits oriented so that (a) their major axes are
pointed toward the Earth and (b) their major axes are perpendicular to=
our
line of sight.

Chapter 18 ___________________________________

If =
no one
has ever seen a star go through the complete formation process, how ar=
e we
able to understand how stars form?

Why=
is it
more difficult to observe the life cycles of stars than the life cycle=
s of
planets or animals?

If =
an
interstellar medium fills the space between the stars, how is that we =
are
able to see the stars at all?

Why=
is
the daytime sky blue? Why are distant mountains purple? Why is the Sun=
red
when seen near the horizon at sunrise or sunset? In what ways are your
answers analogous to the explanations for the bluish color of reflecti=
on
nebulae and the process of interstellar reddening?

=
li>

To =
see
the constellation ComaBerenices (Berenice’s Hair) you must look perpendicular to
the plane of the Milky Way. By
contrast, the Milky Way passes through the constellation Cassiopeia (n=
amed
for a mythical queen).W=
ould
you expect H ll regions to be more abundant in Coma Berenices or in
Cassiopeia? Explain your reasoning.

The
interior of a dark nebula is billions of times less dense than the air
that you breathe.How, t=
hen,
are dark nebulae able to block out starlight?

Why=
are
low temperatures nexessary in order for protostars to form inside dark
nebulae?

Com=
pare
and contrast Barnard objects and Bok globules.How many Sun-sized stars coul=
d you
make out of a Barnard object? Out of a Bok globule?

<=
/li>

Des=
cribe
the energy source that causes a protostar to shine.How does this source differ f=
rom
the energy source inside a main-sequence star?

Wha=
t is
an evolutionary track? How can evolutionary tracks help us interpret t=
he
H-R diagram?

What
happens inside a protostar to slow and eventually halt its gravitation=
al
contraction?

Why=
are
the evolutionary tracks of high-mass stars different from those of
low-mass stars? For which kind of star is the evolutions more rapid? W=
hy?

Why=
are
protostars more easily seen with an infrared telescope than with a
visibe-light telescope?

In =
what
ways is the internal structure of a 1-M. main-sequence star different =
from
that of a 5-M. main-sequence star? From that of a 0.5-M. main-sequence
star? What features are common to all these stars?

=
li>

Wha=
t sets
the limits of the maximum and minimum masses of a main-sequence star?<=
o:p>

Wha=
t are
T Tauri stars? How do we know that they eject matter at high speed? How
does their rate of mass loss compare to that of the Sun?

Wha=
t are
Herbig-Haro objects? Why are they often found in pairs?

Why=
do
disks form around contracting protostars? What is the connection betwe=
en
disks and bipolar outflows?

You=
ng open
clusters like those shown in Figures 188-18 and 18-19 are found only in
the plane of the Galaxy. Explain why this should be.

=

Why=
are
observations at millimeter wavelengths so much more useful in exploring
interstellar clouds than observations at visible wavelengths?

Wha=
t are
giant molecular clouds? What role do these clouds play in the birth of
stars?

Gia=
nt
molecular clouds are among the largest objects in our Galaxy. Why, the=
n,
were they discovered only relatively recently?

Con=
sider
the following stages in the evolution of a young star cluster: (i) H II
region; (ii) dark nebula; (iii) information of O and B stars; (iv) gia=
nt
molecular cloud. Put these stages in the correct chronological order a=
nd
discuss how they are related.

What
is the helium flash? Why does it happen in some stars but not in other=
s?

Why
does a star’s luminosity decrease after helium fusion begins in =
its
core?

Why
does it mean when an astronomer says that a stare “moves” =
from
one place to another on an H-R diagram?

Explain
why the majority of the stars visible through telescopes are main-sequ=
ence
stars.

On
an H-R diagram, main-sequence stars do not lie along a single narrow l=
ine
but are spread out over a band (see figure 19-9b). On the basis of how
stars evolve during their main-sequence lifetimes, explain why this sh=
ould
be so.

Explain
how and why the turnoff point on the H-R diagram of a cluster is relat=
ed
to the cluster’s age.

There
is a good deal of evidence that our universe is about 13.7 billion yea=
rs
old (see chapter 24). Explain why no mains-sequence stars of spectral
class M have yet evolved into red-giant stars.

How
do astronomers know that globular clusters are made of old stars?

=

Red-giant
stars appear more pronounced in composites of infrared images and
visible-light images, like those in figure 19-4b and figure 19-12. exp=
lain
why.

The
horizontal-branch stars in figure 19-12 appear blue. (a) Explain why t=
his
is consistent with the color-magnitude diagram shown in figure 19-123.=
(b)
all horizontal-branch stars were once red giants. Explain what happene=
d to
these stars to change their color.

What
is the difference between population I and population II stars? In what
sense can the stars of one population be regarded as the
“children” of the other population?

Both
diamonds and graphite (the material used in pencils to make marks on p=
aper)
are crystalline forms of carbon. Most of the carbon atoms in these
substances have nuclei with 6 protons and 6 neutrons (12C). Where did
these nuclei come from?

Why
do astronomers attribute the observed Doppler shifts of a Cepheid vari=
able
to pulsation, rather than to some other cause, such as orbital motion?=

Why
do Cepheid stars pulsate? Why are these stars important to astronomers=
who
study galaxies beyond the Milky way?

What
is a roche lobe? What is the inner lagrangian point? Why are roche lob=
es important
in close star systems?

What
is the difference between a detched binary, a semidetached binary, a
contact binary, an overcontact binary?

Massive
main-sequence stars turn into red giants before less massive stars. Wh=
y,
then, is the more massive star in algol a main-sequence star and the l=
ess
massive star a red giant?

Advanced questions

=

&nbs=
p;

The
radius of the sun has increased over the past several billion years. O=
ver
the same time period, the size of the moon’s orbit around the ea=
rth
has also increased. A few billion years ago, were annular eclipses of =
the
sun ( see figure 3-12) more or less common than they are today? Explai=
n.

The
sun has increased in radius by 6% over the past 4.56 billion years. Its
present-day radius is 696,000 km. What was its radius 4.56 billion yea=
rs
old?

Calculate
the escape speed from (a) the surface of the present day sun and (b) t=
he
surface of the sun when it becomes a red giant, with essentially the s=
ame
mass as today but with a radius that is 100 times larger. (c) explain =
how
your results show that a red-giant star can lose mass more easily
thana main-sequence sta=
r.

Calculate
the average speed of a hydrogen atom (mass 1.67x10^-27kg) (a) in the
atmosphere of the present day sun, with temperature 5800k, and (b) in =
the
atmosphere of a 1-M red giant, with temperature 3500 k. (c) compare yo=
ur
results with the escape speeds that you calculated in Q. 27. Use this
comparison to discuss how well the present day 1-M red giant can retain
hydrogen in their atmosphere.

Use
the value of the sun’s luminosity (3.90x10^26 watts, or 3.90x10^=
26
joules per second) calculate what mass of hydrogen the sun will convert
into helium during its entire main-sequence lifetime of 1.2x10^10 year=
s.
(assume that the sun’s luminosity remains nearly constant during=
the
entire 1.2x10^10 years) what fraction does this represent of the total
mass of hydrogen that was originally in the sun?

(a)
the main-sequence stars Sirius (spectral type A1), vega (A0), spica (B=
1),
Fomalhaut (A3), and regulus (B7) are among the 20 brightest stars in t=
he
sky. Explain how you can tell that all these stars are younger than the
sun. (b) the third-brightest star in the sky, although it can be seen =
only
south of 29 degrees north latitude, is alphacentauri A. it is a main-sequ=
ence
star of spectral type G2, the same as the sun. Can you tell from this
whether alpha centauri A is younger than the sun, the same age, or old=
er?
Explain your reasoning.

using
the same horizontal and vertical scales as in figure 19-9a, make point=
s on
an H-R diagram for each of the stars listed in table 19-1. label each
point with the star’s mass and its main-sequence lifetime. Which=
of
these stars will remain on the main sequence after 10^9 years? After 1=
0^11
years?

Explain
why the quantity f in box
19-2 has a different value for stars with masses less t=
han
0.4 M. Than for stars with masses greater than 0.4 M. In which case do=
es f
have a greater value?

Calculate
the main- sequence lifetimes of (a) a 9-M star and(b) a 0.25-M star. Compare th=
ese
lifetimes with that of the sun.

The
earliest fossil records indicate that life appeared on the earth about=
a
billion years after the formation of the solar system. What is the most
mass that a star could have in order that its lifetime on the main
sequence is long enough to permit life to form on one or more of its
planets? Assume that the evolutionary processes would be similar to th=
ose
that occurred on the earth.

As
a red giant, the sun’s luminosity will be about 2000 timesgreater than it is now, so the
amount of solar energy falling on the earth will increase to 2000 times
its present-day value. Hence, to maintain thermal equilibrium, each sq=
uare
meter of the earth’s surface will have to radiate 2000 times as =
much
energy into space as it does now. Use the Stefan-Boltzmann law to
determine what the earth’s surface temperature will be under the=
se
conditions.

When
the sun becomes a red giant, its luminosity will be about 2000 times
greater than it is today. Assuming that this luminosity is caused only=
be
fusion of the sun’s remaining hydrogen, calculate how long our s=
tar
will be a red giant. (In facet only a fraction of the remaining hydrog=
en
will be consumed and the luminosity will vary over time as shown in fi=
gure
19-8.)

What
observations would you make of a star to determine whether its primary
source of energy is hydrogen fusion or helium fusion?

=
li>

The
star whose spectrum is shown in figure 19-15a has a lower percentage of
heavy elements that the sun, whose spectrum is shown in figure 19-15b.
Hence, the star in figure 19-15a has a higher percentage of hydrogen. =
Why
then isn’t the H alpha absorption line of hydrogen noticeably da=
rker
fore the star in figure 19-15?

would
you expect the color of a Cepheid variable star to change during the
star’s oscillation period? If not why not? If so describe why the
color should change, and describe the color changes you would expect to
see during an oscillation period.

The
brightness of a certain Cepheid variable star increases and decreases =
with
a period of 10 days . (a) what must this star’s luminosity be if=
its
spectrum has strong absorption lines of hydrogen and helium, but no st=
rong
absorption lines of heavy elements? (b) repeat part (a) for the case in
which the star’s spectrum also has strong absorption lines of he=
avy
elements.

The
star X arietis is an RR Lyrae variable. Its apparent brightness caries
between 2.0x10^-15 and 4.9x10^-151 that of the sun with a period of .65
day. Interstellar extinction dims the star by 37%. Approximately how f=
ar
away is the star?

The
apparent brightness of alpha Cephei (a type I Cepheid variable) varies
with a period of 5.4 days. Its average apparent brightness is 5.1x10^-=
13
that of the sun. Approximately how far away is alpha cephei?

suppose
you find a binary star system in which the more massive star is a red
giant and the less massive star is a main-sequence star. Would you exp=
ect
that mass transfer between the stars has played an important role in t=
he
evolution of these stars? Explain your reasoning.

the
larger star in the algol binary system (see figure 19-21a) is of spect=
ral
class K, While the smaller star is of spectral class B. Discuss how the
color of algol changes as seen through small telescope (through which
algol appears as a ingle star) what is the color during a deep eclipse,
when the large star eclipses the small one? What is the color when the
small star eclipses the large one?

suppose
the detached star in B lyrae (figure 19-21b) did not have an accretion
disk. Wouldthe deeper d=
ips in
the light curve be deeper , shallower, or about the same?

=
u>

The
two stars that make up the overcontract binary W ursae Marjoris (figure
1-c) have estimated masses of 0.9 M and 0.62 M. (a) find the average
separation between the two stars. Give your answer in kilometers. (b) =
the
radii of the two stars are estimated to be 1.14 R and 0.83 R. Show that
these values and your result n part (a) are consistent with the statem=
ent
that this is an overcontact binary.

The
stars that make up the binary system W ursae Majoris (se figure 19-21c)
have particularly strong magnetic fields. Explain how astronomers could
have discovered this.

Chapter
23___________________________________

1. Why do the stars of the Galaxy appear to form a =
bright
band that extends around the sky?

2. How did interstellar extinction mislead astronom=
ers
into believing that we are at the center of our Galaxy?

3. How did observations of globular clusters help
astronomers determine our location in the Galaxy?

4. What are RR Lyrae stars?

&nbs=
p; Why
are they useful for determining the distance from our solar system to the
center of the Galaxy?

5. Why are infrared telescopes useful for exploring=
the
structure of the Galaxy?

&nbs=
p; Why
is it important to make observations at both near-infrared and far-infrared
wavelengths?

6. The galactic halo is dominated by Population II =
stars,
whereas the galactic disk contains predominantly Population I stars.In which of these parts of the Gal=
axy
has star formation taken place recently?

&nbs=
p; Explain.

<=
/u>

7. O or B main-sequence stars are found in the gala=
ctic
disk but not in globular clusters.Why is this so?

8. What must happen within a hydrogen atom for it t=
o emit
a photon of wavelength 21 cm?

13. Many classic black-and-white photographs of spi=
ral
galaxies were taken using film that was most sensitive to blue light.Explain why the spiral arms were
particularly prominent in such photographs.

14. What kinds of objects (other than H I clouds) do
astronomers observe to map out the Galaxy’s spiral structure?

19. Another student tells you that the Milky Way Ga=
laxy
is made up “mostly of stars.”&=
nbsp;
Is this statement accurate?

&nbs=
p; Why
or why not?

20. What is the difference between dark matter and =
dark
nebulae?

21. What proposals have been made to explain the na=
ture
of dark matter?

&nbs=
p; What
experiments or observations have been made to investigate these proposals?<=
o:p>

&nbs=
p; What
are the results of this research?

22. What is the winding dilemma?

&nbs=
p; What
does it tell us about the nature of spiral arms?

23. Do density waves form a stationary pattern in a
galaxy?

&nbs=
p; If
not, do they move more rapidly, less rapidly, or at the same speed as stars=
in
the disk?

24. In our Galaxy, why are stars of spectral classe=
s O
and B only found in or near the spiral arms?

&nbs=
p; Is
the same true for stars of other spectral classes?

&nbs=
p; Explain
why or why not.

25. Compare the kinds of spiral arms produced by de=
nsity
waves with those produced by self-propagating star formation.By examining Figure 23-16, cite ev=
idence
that both processes may occur in our Galaxy.

26. What is the evidence that there is a super mass=
ive
black hole at the center of our Galaxy?

&nbs=
p; How
is it possible to determine the mass of this black hole?

27. What is the evidence that material has been fal=
ling
into super massive black hole at the galactic center?

Chapter 23

Advanced Questions

28. =
Discuss how the Milky Way would appear to us if =
the
Sun were relocated to (a) the edge of the Galaxy; (b) the galactic halo; (c)
the galactic bulge.

29. =
Explain why globular clusters spend most of their
time in the galactic halo, even though their eccentric orbits take them clo=
se
to the galactic center.

30. =
The disk of the Galaxy is about 50 kpc in diamet=
er
and 600 pc thick. (a) Find the volume of the disk in cubic parsecs. (b) Find
the volume (in cubic parsecs) of a sphere 300 pc in radius centered on the =
Sun.
(c) If supernovae occur randomly throughout the volume of the Galaxy, what =
is
the probability that a given supernova will occur within 300 pc of the
Sun?If there are about three
supernovae each century in our Galaxy, how often, on average, should we exp=
ect
to see one within 300 pc of the Sun?

31. =
An RR Lyrae star whose peak luminosity is 100 L<=
sub>☼
is in a globular cluster.At =
its
peak luminosity, the star appears from the Earth to be only 1.47 x10-1=
8
as bright as the Sun.Determi=
ne the
distance to this globular cluster (a) in AU and (b) in parsecs.

<=
/u>

32. =
A typical hydrogen atom in interstellar space
undergoes a spin-flip transition only once every 107 years.How, then, is it at all possible to
detect the 21-cm radio emission from interstellar hydrogen?

<=
/p>

33. =
Calculate the energy of the photon emitted when a
hydrogen atom undergoes a spin-flip transition.How many such photons would it tak=
e to
equal the energy of a single Ha
photon of wavelength 656.3 nm?

34. =
Suppose you were to use a radio telescope to mea=
sure
the Doppler shift of 21-cm radiation in the plane of the Galaxy. (a) If you
observe 21-cm radiation from clouds of atomic hydrogen at an angle of 45&or=
dm;
from the galactic center, you will see the highest Doppler shift from a clo=
ud
that is as far from the galactic center as it is from the Sun.Explain this statement using a dia=
gram.
(b) Find the distance from the Sun to the particular cloud mentioned in (a)=
.

35. =
Calculate approximately how many times our solar
system has orbited the center of our Galaxy since the Sun and planets were
formed 4.56 x 109 years ago.

36. =
Sketch the rotation curve you would obtain if the
Galaxy were rotating like a rigid body.

37. =
The mass of our Galaxy interior to the Sun’=
;s
orbit is calculated from the radios of the Sun’s orbit and its orbital
speed.By how much would this
estimate be in error if the calculated distance to the galactic center were=
off
by 10%?By how much would this
estimate be in error if the calculated orbital velocity were off by 10%? Explain your reasoning.

=

38. =
A gas cloud located in the spiral arm of a dista=
nt
galaxy is observed to have an orbital velocity of 400 km/s.If the cloud is 20,000 pc from the
center of the galaxy and is moving in a circular orbit, find (a) the orbital
period of the cloud and (b) the mass of the galaxy contained within the clo=
ud’s
orbit.

39. =
According to the Galaxy’s rotation curve in
Figure 23-18, a star 16 kpc from the galactic center has an orbital speed of
about 270 km/s.Calculate the=
mass
within that star’s orbit.

40. =
Speculate on the reasons for the rapid rise in t=
he
Galaxy’s rotation curve (see Figure 23-18) at distances close to the
galactic center.

41. =
Show that the form of Kepler’s third law
stated in Box=
23-2,
P2 =3D 4p2=
a3/G(M+M☼),
is equivalent to M =3D rv2/G, provided the orbit is a circle. (Hint: The mass of the Sun (M&=
#9788;)
is much less than the mass of the Galaxy inside the Sun’s orbit (M).)=

42. =
The image below shows the spiral galaxy M74, loc=
ated
about 55 million light-years from the Earth in the constellation Pisces (the
Fish).It is actually a
superposition of two false-color images: The red portion is an optical image
taken at visible wavelengths, while the blue portion is an ultraviolet image
made by NASA’s Ultraviolet Imaging Telescope, which was carried into
orbit by the space shuttle Col=
umbia
during the Astro-1 mission in 1990.Compare the visible and ultraviolet images and, from what you know a=
bout
stellar evolution and spiral structure, explain the differences you see.

43. =
The figure at the bottom of this page shows infr=
ared
images of the two spiral galaxies.Explain which of these is a grand-design spiral galaxy and which is a
flocculent spiral galaxy.Exp=
lain
your reasoning.

44. =
(a) Calculate the Schwarzschild radius of a
supermassive black hole of mass 3.7 x 106 M☼, t=
he
estimated mass of the black hole at the galactic center.Give our answer in both kilometers=
and
astronomical units. (b) What is the angular diameter of such a black hole as
seen at a distance of 8 kpc, the distance from the Earth to the galactic
center?Give your answer in
arcseconds.Observing and obj=
ect
with such a small angular size will be a challenge indeed!(c) What is the angular diameter o=
f such
a black hole as seen from a distance of 45 AU, the closest that the star SO=
-16
comes to Sagittarius A*? Again, give your answer in arcseconds.Would it be discernible to the nak=
ed eye
at that distance? (A normal human eye can see details as small as about 60
arcseconds.)

45. =
(a) The scale bar in Figure 23-27 shows that at =
the
distance of Sagittarius A*, a length of 1600 AU has an angular size of 0.2
arcsecond.Use this informati=
on to
calculate the distance to Sagittarius A*. (b) The star SO-16 moves around
Sagittarius A* in an elliptical orbit with semimajor axis 1680 AU.Use this and the information given=
in
the caption to Figure 23-27 to find the orbital period of SO-16. (c) Given =
the
period and the semimajor axis of the star’s orbit, is it possible to
calculate the mass of SO-16 itself?If it is, explain how this could be done; if not, explain why not.

46. =
The stars S0-2 and S0-19 orbit Sagittarius A* wi=
th
orbital periods of 14.5 and 37.3 years, respectively. (a) Assuming that the supermassive =
black
hole in Sagittarius A* has a mass of 3.7 x 106 M☼,
determine the semimajor axes of the orbits of these two stars.Give your answers in AU. (b) Calcu=
late
the angular size of each orbit’s semimajor axis as seen from the
Earth.(See Section 23-1 for =
the
distance from the Earth to the center of the Galaxy.) Explain why extremely
high-resolution infrared images are required to observe the motions of these
stars.

47. =
Consider a star that orbits around Sagittarius A=
* in
a circular orbit of radius 530 AU. (a) If the star’s orbital speed is
2500 km/s, what is its orbital period?&nbs=
p;
Give your answer in years.(b) Determine the sum of the masses of Sagittarius A* and the star.<=
span
style=3D'mso-spacerun:yes'> Give your answer in solar masses.<=
span
style=3D'mso-spacerun:yes'> (Your answer is an estimate of the=
mass
of Sagittarius A*, because the mass of a single star is negligibly small by
comparison.)

Chapter 24____________________________=
____

Review Questions:

=
1.Why
did many nineteenth-century astronomers think that the “spiral nebula=
e”
are part of the Milky Way?

=
2.What
was the Shapley-Curtis “debate” all about? Was a winner declare=
d at
the end of the “debate”? Whose ideas turned out to be correct?<=
o:p>

=
3.How
did Edwin Hubble prove that the Andromeda “Nebula” is not a neb=
ula
within our Milky Way Galaxy?

=
4.Are
any galaxies besides our own visible with the naked eye from Earth? If so,
which one(s)?

=
5.An
educational publication for children included the following statement:
“The Sun is in fact the only star in our galaxy. All of the other sta=
rs
in the sky are located in other galaxies.” How would you correct this
statement?

=
6.What
is the Hubble classification scheme? Which category includes the largest
galaxies? Which includes the smallest? Which category of galaxy is the most
common?

=
7.Which
is more likely to have a blue color, a spiral galaxy or an elliptical galax=
y?
Explain why.

=
8.Which
types of galaxies are most likely to have new stars forming? Describe the
observational evidence that supports your answer.

=
9.Explain
why the apparent shape of an elliptical galaxy may be quite different from =
its
real shape

=
10.Wh=
y do
astronomers suspect that the Hubble tuning fork diagram does not depict the
evolutionary sequence of galaxies?

=
11.Wh=
y are
Cephid variable stars useful for finding the distances to galacies? Are the=
re
any limitations on their use for this purpose?

=
12.Wh=
y are TypeIa=
supernovae useful for finding the distances to very remote galaxies? Can th=
ey
be used to find the distance to any galaxy you might choose? Explain.

<=
/o:p>

=
13.Wh=
at is the
Tully-Fisher relation? How is it used for measuring distances? Can it be us=
ed
for galaxies of all kinds? Why or why not?

=
14.Wh=
at are
maser? How can they be used to measure the distance to a galaxy?

=

=
15.Wh=
at is
the Hubble law? How can it be used to determine distances?

=
p>

=
16.Ho=
w did
the discovery of the Hubbl Law reinforce the idea that the spiral
“nebulae” could not be part of the Milky Way?

=
17.Wh=
y do
you suppose it has been so difficult to determine the value of H0?

=
18.So=
me
galaxies in the Local Group exhibit blueshifted spectral lines. Why
aren’t these blueshifts violations of the Hubble law?

<=
/p>

=
19.Wh=
at are
the differences between regular and irregular clusters?

=
20.Wh=
at is
the difference between a cluster and a supercluster? Are both clusters and
superclusters held together by their gravity?

=
21.Wh=
at
measurements to astronomers make to construct three-dimensional maps of the
positions of galaxies in space?

=
22.De=
scribe
what voids are and what they tell us about the large-scale structure of the
universe.

=
23.Wh=
y is
the intracluster gas in galaxy clusters at such high temperatures.?

=
24.Wh=
at are
starburst galaxies? How can the be produced by collisions between galaxies?=

=
26.Wh=
at evidence
is there for the existence of dark matter in clusters of galacies?

=
27.Wh=
at is
gravitational lensing? Why don’t we notice the gravitational lensing =
of
light by ordinary objects on Earth?

=
28.Ho=
w do
observations of galaxy cluster 1E0657-56 help constrain the nature of dark
matter?

=
29.Wh=
at
observations suggest that present-day galaxies formed from smaller assembla=
ges
of matter?

=
30.On=
what
grounds do astronomers think that in the past, spiral galaxies were more
numerous in rich clusters than they are today? What could account for this
excess of spiral galaxies in the past?

Advanced Questions:

=

=
31.Hu=
bble
made his observations of Cepheids in M31 using the 100-inch (2.5 meter)
telescope on Mount Wilson. Completed in =
1917,
this was the largest telescope in the world when Hubble carried out his
observations in 1923. Why was it helpful to use such a large telescope?

=
32.The
image on page 665 shows the Small Magellanic Cloud (SMC), an irregular gala=
xy
that orbits the Milky Way. The SMC is 63 kpc (200,000 ly) from Earth and 8 =
kpc
(26,000 ly) across, and can be seen with the naked eye from southern latitu=
des.
What features of this image indicate that there has been recent star format=
ion
in the SMC?Explain.

=
33.Wh=
en the
resultf from the Hipparcos mission were release, with new and improved
measurements of the parallaxes of nearby stars within 500 pc,
astronomers had to revise the distances to many remote galaxies of
millions of parsecs away. Explain why.

=
34.As
Figure 19-19 shows, there are two types of Cepheid variables. Type I Cephei=
ds
are metal-rich stars of Population I, while Type II Cepheids are metal-poor
stars of Population II. A) Which type of Cepheid variables would you expect=
to
be found in globular clusters? Which type would you expect to be found in t=
he
disk of a spiral galaxy? Explain your reasoning. B) When Hubble discovered
Cepheid variables in M31, the distinction between Type I and Type II Cephei=
ds
was not yet known. Hence, Hubble thought that the Cepheids seen in the disk=
of
M31 were identical to those seen in globular clusters in our own galaxy. As=
a
result, his calculations of the distance to M31 were in erroe. Using Figure
19-19, explain whether Hubble’s calculated distance was too small or =
too
large.

*35. Astronomers often =
state
the distance to a remote galaxy in terms of its distance modulus, which is =
the
difference between the apparent magnitude m and the absolute magnitu=
de M
(see Box 17-3=
).
A) By measuring the brightness of supernova 1994I in the galaxy M51 (see Fi=
gure
24-2), the distance modulus for this galaxy was determined to be m-M=
=3D
29.2. Find the distance to M51 in megaparsecs (Mpc). B) A separate distance
determination, which involved measuring the brightnesses of planetary ebebu=
lae
in M51, found m-M =3D 29.6. What is the distance to M51 that you cal=
culate
from this information? C) What is the difference between your answers to pa=
rts
(a) and (b)? Compare this difference with the 750-kpc distance from the Ear=
th
to M31, the Andromeda Galaxy. The difference between your answers illustrat=
es
the uncertainties involved in determining the distances to galaxies!

=
o:p>

*36. Suppose you discov=
er a
Type Ia supernova in a distant galaxy. At maximum brilliance, the supernova
reaches an apparent magnitude of +10. How far away is the galaxy? (Hint<=
/i>:
See Box 24-1<=
/st1:address>.)

=
37.The
masers that orbit the center of the spiral galaxy M106 travel at an orbital
speed of about 1000 km/s. Astronomers observed these maser at intervals of 4
months. A) What distance does a single maser move during a 4-month period? =
Give
your answer in kilometers and in AU. B) During this period, a maser moving
across the line of sight (like the maser shown in green in Figure 24-15)
appeared to move through an angle of only 10^-5 arsec. Calculate the distan=
ce
to the galaxy.

=
38.Th=
e average
radial velocity of galaxies in the Hercules cluster pictured in Figure 24-1=
8 is
10,800 km/s.A) Using H0 =3D =
73
km/s/Mpc, find the distance to this cluster. Give your answer in megaparsecs
and in light-years. B) How would your answer to (a) differ if the Hubble
constant had a smaller value? A larger value? Explain.

=
39.A
certain galaxy is observed to be receding from the Sun at a rate of 7500 km=
/s.
The distance to this galaxy is measured independently and found to be 1.4 x
10^8 pc. From these data, what is the value of the Hubble constant?

*40. In the spectrum of=
the
galaxy NGC 4839, the K line of singly ionized calcium has a wavelength 403.2
nm. A) What is the redshift of this galaxy? (Hint: See Box 24-2) B)
Determine the distance to this galaxy using the Hubble law with H0 =3D 73
km/s/Mpc.

*41. The galaxy RD1 has=
a
redshift of z =3D 5.34. A) Determine its recessional velocity v in k=
m/s
and as a fraction of the speed of light. B) What recessional velocity would=
you
have calculated if you had erroneously used the low-speed formula relating =
z
and v? Would using this formula have been a small or large error? C)
According to the Hubble law, what is the distance from Earth to RD1? Use H0=
=3D
73 km/s/Mpc for the Hubble constant, and give your answer in both megaparse=
cs
and light-years.

42. It is estimated tha=
t the
Coma cluster (see Figure 24-21) contains about 10^13 Mo of intracluster gas=
. A)
Assuming that this gas is made of hydrogen atoms, calculate the total numbe=
r of
intracluster gas atoms in the Coma cluster. B) The Coma cluster is roughly
spherical in shape, with a radius of about 3 Mpc. Calculate the number of
intracluster gas atoms per cubis centimeter in the Coma cluster. Assume that
the gas fills the cluster uniformly. C) Compare the intracluster gas in the
Coma cluster with the gas in our atmosphere (3 x 10^19 molecules per cubic
centimeter, temperature 300 K); a typical gas cloud within our own Galaxy (a
few hundred molecules per cubic centimeter, temperature 50 K or less); and =
the
corona of the Sun (10^5 atoms per cubic centimeter, temperature of 10^6 K).=

*43. Two galaxies separ=
ated by
600 kpc are orbiting each other with a period of 40 billion years. What is =
the
total mass of the two galaxies?

*44. Figure 24-29 shows=
the
rotation curves of the Sa galaxy NGC 4378. Using data from that graph,
calculate the orbital period of stars 20 kpc from the galaxy’s center.
How much mass lies within 20 kpc from the center of NGC 4378?

45. How might you deter=
mine
what part of a galaxy’s redshift is caused by the galaxy’s orbi=
tal
motion about the center of mass of its cluster?

46. The accompanying im=
age
shows the unusual elliptical galaxy NGC 5128. Explain how the properties of
this galaxy seen in the infrared image can be explained if NGC 5128 is the
result of a merger of an elliptical galaxy and a spiral galaxy.

=

47. Explain wy the dark=
matter
in galaxy clusters could not be neutral hydrogen.

48. According to Figure=
24-34c,
elliptical galaxies continue to form stars for about a billion years after =
they
form. Give an argument why we might expect to find some Population I stars =
in
an elliptical galaxy. (Hint: Table 19-1 gives the mainsequence lifet=
imes
for stars of different masses.)

Chapter 25____________________________=
__

Review Questions:

=
1.When
quasi-stellar radio sources were first discovered and named, why were they
called “quasi-stellar”?

=
2.How
were quasars first discovered? How was it discovered that they are very dis=
tant
objects?

=
3.Explain
why astronomers cannot use any of the standard candles describe in Section =
24-4
to determine the distances to quasars.

=
4.Suppose
you saw an object in the sky that you suspected might be a quasar. What sor=
t of
observations might you perform to test your suspicion?

=
5.Quasar
PC 1247 + 3406 is presently about 25.9 billion light-years from Earth. Expl=
ain
how it is possible for astronomers to see this quasar, even though light
travels at a speed of 1 light-year per year.

=
6.How
does the spectrum of a quasar differ from that of an ordinary galaxy? How do
spectral lines help astronomers determine the distances to quasars?

=
7.If
quasars lie at the centers of galaxies, why don’t we see strong
absorption lines from the galaxy’s stars when we look at the spectrum=
of
a quasar (like those shown in Figures 25-3 and 25-4)?

=
8.It
was suggested in the 1960s that quasars might be compact objects ejected at
high speeds from the centers of nearby ordinary galaxies. Explain why the
absence of blueshifted quasars disproves this hypothesis.

=
9.Why
were some astronomers skeptical that he redshifts of quasars gave a true
indication of their distance?

=
10.Ho=
w do
astronomers know that quasars are located in galaxies? In what sorts of
galaxies are they found?

=
11.Wh=
at is
a Seyfert galaxy? Why do astronomers think that Seyfert galaxies may be rel=
ated
to radio-quiet quasars?

=
12.Wh=
at is
a radio galaxy? What is a double radio source? Why do astronomers think the=
se
objects may be related to radio-loud quasars?

=
13.How
would you distinguish between thermal and nonthermal radiation?

<=
/u>

=
14.Wh=
at is the
difference between polarized and unpolarized radiation? How does the
polarization of radiation from M87’s jet show that the radiation is
nonthermal radiation?

=
15.Wh=
at are
head-tail sources? How do they provide evidence that double radio sources
include jets of fast-moving particles?

=
16.Wh=
at is
a blazer? What is unique about its spectrum? How is it related to other act=
ive
galaxies?

=
17.So=
me
blazers or quasars appear to be ejecting material at speeds faster than lig=
ht.
Is the material really moving that fast? If so, how is this possible? If no=
t,
why does the material appear to be traveling so fast?

=
18.Wh=
at do
astronomers learn from the widths of the spectral lines of quasars?

=
19.Wh=
at do
the brightness fluctuations of a particular active galaxy tell us about the
size of the energy-emitting region within that galaxy?

=
20.How
could a supermassive black hole, from which nothing – not even light
– can escape, be responsible for the extraordinary luminosity of a
quasar?

=
21.Wh=
at is
the Eddington limit? Explain how it can be used to set a limit on the mass =
of a
supermassive black hole, and explain why this limit represents a minimum ma=
ss
for the black hole.

=
22.Ex=
plain
how the rotation curve of a galactic nucleus can help determine whether a
supermassive black hole is present.

=
24.Ex=
plain
how the unified model of active galaxies suggests that quasars, blazers, and
radio galaxies are the same kind of object viewed from different angles.

=
25.Wh=
y do
you suppose there are no quasars relatively near our Galaxy?

=

Advanced Questions:

=

=
26.Wh=
en we
observe a quasar with redhisft z =3D 0.75, how far into its past are=
we looking?
If we could see that quasar as it really is right now (that is, if the light
from the quasar could somehow reach us instantaneously), would it still look
like a quasar? Explain why or why not.

*27. The quasar SDSS 10=
44-0125
has a redshift z =3D 5.80. At what speed does this quasar seem to be recedi=
ng
from us? Give your answer in km/s and as a fraction of the speed of light c=
.

*28. Suppose that an as=
tronomer
discovers a quasar with a redshift of 8.0. With what speed would this quasar
seem to be receding from us? Give your answer in km/s and as a fraction of =
the
speed of light.

29. In the quasar spect=
rum
shown in Figure 25-4, there are many deep absorption lines to the left of t=
he L
emission line (that is, at shorter wavelengths). These lines, collectively
called the Lyman-alpha forest, are due to remote gas clouds along our
line of sight to the quasar. Hydrogen atoms in these clouds absorb L(alpha)
photons from the quasar. Explain why the L (alpha) absorption lines due to
these clouds are at shorter wavelengths than the L (alpha) emission line fr=
om
the quasar itself.

30. Explain how the exi=
stence
of gravitational lenses involving quasars (review Section 24-8) constitutes
evidence that quasars are located at the great distances inferred from the
Hubble law.

31. The Seyfert galaxy =
NGC 1275
is actually two galaxies that are colliding. Images of NGC 1275 show a numb=
er
of globular clusters with a distinctive blue color. Explain how this color
shows that these clusters formed relatively recently, perhaps as a result of
the collision.

32. In the image that o=
pens
this chapter, the close-up view of the Cygnus A jet shows that different
wavelengths are preferentially emitted at different locations along the
jet’s length. Explain why, using the following principle: As an
individual particle moves in a magnetic field, the greater its speed, the
shorter the wavelength of the synchrotron radiation that it emits.

33. Suppose the distanc=
e from
point A to point B in Figure 25-14a is 26 light-years and the blob moves at
13/15 of the speed of light. As the blob moves from A to B, it moves 24
light-years toward the Earth and 10 light-years in a transverse direction. =
A)
How long does it take the blob to travel from A to B? B) If the light from =
the
blob at A reaches Earth in 2020, in what year does the light from B reach
Earth? C) As seen from Earth, at what speed does the blob appear to move ac=
ross
the sky?

*34. Suppose a blazer a=
t z =3D
1.00 goes through a fluctuation in brightness that lasts one week (168 hour=
s)
as seen from Earth. A) At what speed does does the blazer seem to be moving
away from us? B) Using the idea of time dilation, determine how long this
fluctuation lasted as measured by an astronomer within the blazar’s h=
ost
galaxy. C) What is the maximum size (in AU) of the region from which this
blazer emits energy?

=
35.A)
Calculate the maximum luminosity that could be generated by accretion onto a
black hole of 3.7 x 10^6 solar masses. (This is the size of the black hole
found at the center of the Milky Way, as described in Section 25-6.) Compare
this to the total luminosity of the Milky Way, about 2.5 x 10^10 L..B)
Speculate on what we might see if the center of our Galaxy became an active
galactic nucleus with the luminosity you calculated in (a).

=

*36. Observations of a =
certain
galaxy show that stars at a distance of 16 pc from the center of the galaxy
orbit the center at a speed of 200 km.s. Use Newton’s form of Kepler’s t=
hird
law to determine the mass of the central black hole.

*37. Calculate the
Schwarzschild radius of a 10^9-solar-mass black hole. How does your answer
compare with the size of our solar system (given by the diameter of
Pluto’s orbit)?

38. Figure 25-9 shows t=
he
double radio source Centaurus A. Is it possible that somewhere in the unive=
rse
there is an alien astronomer who observes this same object as a blazer? Exp=
lain
your answer with a drawing showing the relative positions of the Earth, the
alien astronomer, and Centaurus A.

Chapter 28

Review Questions:

1.Why are extreme life-forms on Earth, such as
those shown in the photograph that opens this chapter, of interest ot
astrobiologists?

What
is meant by “life as we know it”? Why do astrobiologists
suspect that extraterrestrial life is likely to be of this form?

<=
/o:p>

How
have astronomers discovered organic molecules in interstellar space? D=
oes
this discovery mean that life of some sort exists in the space between=
the
stars?

Mercury,
Venus, and the Moon are all considered unlikely places to find life. Suggest why this should be.

Many
science-fiction stories and movies—including The War of the
Worlds, Invaders from Mars, Mars Attacks!, and Martians, Go Home—=
;involve
invasions of Earth by intelligent beings from Mars.Why Mars rather than any of t=
he
other planets?

Summarize
the differences in philosophy between the biological experiments on bo=
ard
the Viking Landers and those on board Beagle 2

What
arguments can you give against the idea that the “face” on
Mars (Figure 28-8) is of intelligent origin?What arguments can you give in
favor of this idea?

Suppose
someone brought you a roc that he claimed was a Martian meteorite.What scientific tests would y=
ou
recommend be done to test this claim/

Why
are most searches for extraterrestrial intelligence made using radio t=
elescopes?Why are most of these carried=
out
at frequencies between 10^3 MHz and 10^4 MHz?

Explain
why infrared telescopes like those proposed for Darwin and Terrestrial Planet Find=
er
need to be placed in space.

Advanced Questions:

In
1802, when it seemed likely to many scholars that there was life on Ma=
rs,
the German mathematician Karl Friedrich Gauss proposed that we signal =
the
Martian inhabitants by drawing huge geometric patterns in the snows of=
Siberia.His plan was never carried out.(a) Suppose patters had been =
drawn
that were 1000 km across. What
minimum diameter would the objective of a Martian telescope need to ha=
ve
to be able to resolve these patters? Assume that the observations are =
made
at a wavelength of 550 nm, and assume that Earth and Mars are at their
minimum separation.(b)
Ideally, the patters used would be ones that could not be mistaken for
natural formations.They
should also indicate that they were created by an advanced
civilization.What sort =
of
patters would you have chosen?

Assume
that all the terms in the Drake equation have the values give in the t=
ext,
except for N and L. (a) If there are 1000 civilizations in the Galaxy
today, what must be the average lifetime of a technological civilizati=
on?
(b) What is there are a million such civilizations?

(a)
Of the visually brightest stars in the sky listed in Appendix 5, which
might be candidates for having Earthlike planets on which intelligent
civilizations have evolved? Explain your selection criteria.(b) Repeat part (a) for the n=
earest
stars, listed in Appendix 4.

It
has been suggested that extraterrestrial civilizations would choose to
communicate at a wavelength of 21 cm.=
Hydrogen atoms in interstellar space naturally emit at this
wavelength, so astronomers studying the distribution of hydrogen around
the Galaxy would already have their radio telescopes tuned to receive
extraterrestrial signals. (a)
Calculate the frequency of this radiation in megahertz.Is this inside or outside the=
water
hole?(b) Discuss the me=
rits
of this suggestion.

Imagine
that a civilization in another planetary system is sending a radio sig=
nal
toward Earth.As our pla=
net
moves in its orbit around the Sun, the wavelength of the signal we rec=
eive
will change due to the Doppler effect.This gives SETI scientists a =
way to
distinguish stray signals of terrestrial origin (which will not show t=
his
kind of wavelength change) from interstellar signals.(a) Use the data in Appendix =
1 to
calculate the speed of the Earth in its orbit.For simplicity, assume the or=
bit is
circular.(b) If the ali=
en
civilization is transmitting at a frequency of 3000 MHz, what waveleng=
th
(in meters) would we receive if the Earth were moving neither toward n=
or
away from their planet? (c) The maximum Doppler shift occurs if the Ea=
rth’s
orbital motion takes it directly toward or directly away from the alien
planet.How large is tat
maximum wavelength shift? Express your answer both in meters ad as a
percentage of the unshifted wavelength you found in (b).(d) Discuss why it is importa=
nt
that SETI radio receivers be able to measure frequency and wavelength =
to
very high precision.

Astronomers
have proposed using interferometry to make an extremely high-resolution
telescope.This proposal
involves placing a number of infrared telescopes in space, separating =
them
by thousands of kilometers, and combining the light from the individual
telescopes.One design o=
f this
kind has an effective diameter of 6000 km and uses infrared radiation =
with
a wavelength of 10 mm.I=
f it
is used to observe an Earth-like planet orbiting the star Epsilon Erid=
ani,
3.22 parsecs (10.5 light-years) from Earth, what is the size of the
smallest detail that this system will be able to resolve on the face of
that planet? Give your answer in kilometers.